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Agricultural Practices and Environmental Impacts of Aztec and Pre-Aztec Central Mexico

Summary and Keywords

The Basin of Mexico is a key world region for understanding agricultural intensification and the development of ancient and historic cities and states. Archaeologists working in the region have had a long-standing interest in understanding the dynamics of interactions between society and environment and their research has been at the forefront of advances in both method and theory. The Basin of Mexico was the geopolitical core of the Aztec empire, the largest state in the history of Mesoamerica. Its growth was sustained by a complex economy that has been the subject of much research.

Two themes underlie a broad interest in the pre-Hispanic agriculture of the Basin of Mexico. First, how with a Neolithic technology did the Aztecs and their predecessors sustain the growth of large cites, dense rural populations, and the largest state system in the history of pre-Hispanic Mesoamerica? Second, what is the relationship of agricultural intensification and urbanization and state formation? Mesoamerica is the only world region where primary civilizations developed that lacked domestic herbivores for either food or transportation. Their farming depended entirely on human labor and hand tools but sustained large cities, dense populations, and complex social institutions. Intensive agriculture began early and was promoted by risk, ecological diversity, and social differentiation, and included irrigation, terracing, and drained fields (chinampas). Most farming was managed by smallholder households and local communities, which encouraged corporate forms of governance and collective action. Environmental impacts included erosion and deposition, but were limited compared with the degradation that took place in the colonial period.

Keywords: Mesoamerica, Aztec, agriculture, agricultural intensification, irrigation, chinampas, Basin of Mexico, terracing

The Aztec empire began as a military alliance among three city-states, Texcoco, Tenochtitlan, and Tlacopan, in the early 1400s to consolidate control over the Basin of Mexico in the central highlands of Mexico. By the early 16th century the empire dominated by the Mexica of Tenochtitlan had expanded into the southern highlands of Mexico, the tropical Gulf Coast, and the cacao-growing lands of the Pacific Coast to become the largest state in pre-Hispanic Mesoamerica (Figure 1).

Agricultural Practices and Environmental Impacts of Aztec and Pre-Aztec Central MexicoClick to view larger

Figure 1. The Basin of Mexico showing Major Aztec sites.

Drawn by Kristin Sullivan.

It encompassed a great deal of ecological and cultural diversity and large populations. Central Mexico had a population of 3–4.5 million people (Smith, 2012, p. 62) The Basin of Mexico was especially densely settled with over one million people living there. Its capital city located on an island in a lake on the Basin’s floor had a population of at least 80,000 to perhaps over 150,000 people (Evans, 2013, p. 349; Rojas, 2017). Although Tenochtitlan was by far the largest, it was not the only city in the Basin of Mexico (Berdan, 2014; Smith, 2017). The Aztec empire was the last in a series of large and influential pre-Hispanic cities and states in the central highlands.

Sustaining large urban populations and a densely settled rural country side depended on a complex economy that has been the subject of much research in recent decades (Nichols et al., 2017). Full-coverage archaeological settlement pattern surveys in the 1960s and 1970s revealed the previously unrecognized high density of rural Aztec villages and documented broad patterns of settlement and agricultural land use and their history from the Formative through Late Postclassic (Gorenflo & Garraty, 2017; Sanders et al., 1979). The surveys laid the foundation for a series of long-term archaeological investigations of provincial towns, rural villages, and agricultural features (Nichols, 2004). A related focus on household archaeology has shown that pre-Hispanic households often combined farming with craft specialization and multicrafting was common (DeLucia, 2017).

This discussion focuses on Aztec agricultural intensification and the Postclassic period in the Basin of Mexico (for the Formative and Classic periods see Nichols, 2015, 2016) (Figure 2).

Agricultural Practices and Environmental Impacts of Aztec and Pre-Aztec Central MexicoClick to view larger

Figure 2. Basin of Mexico archaeological periods.

Drawn by Kristin Sullivan.

The discussion is organized around two major issues underlying a broader interest in pre-Hispanic agriculture. First, how with a Neolithic technology and no domestic herbivores for food or transport did the Aztecs and their predecessors sustain the growth of large cites, dense rural populations, and the largest state system in the history of prehispanic Mesoamerica? Second, what roles did agricultural intensification play in Aztec urbanism and state formation? Small-scale irrigation began early in the northern Basin of Mexico by the Middle Formative and intensification paralleled the development of large-scale societies. Archaeologists and other scholars in the mid-20th century were drawn to the Basin of Mexico, to test theories about the role of hydraulic agriculture in political centralization and models of cultural ecology and evolution. The late 20th century began a diversification in theoretical perspectives, but this remains an important issue (Scarborough, 2012).

Investigating Pre-Hispanic Agriculture in the Basin of Mexico

An explicit goal of the settlement patterns surveys was to reconstruct the history of pre-Hispanic agriculture (Sanders et al., 1979). Where agricultural features such as terraces were detectable and accessible on the surface and in proximity to sites of a single time period they were dated by association. This approach worked well in areas only occupied late by the Aztecs, but even in these situations distinguishing the early colonial period from pre-Conquest features was not always possible. When agricultural features were present at sites with occupations spanning multiple periods dating by association was not feasible.

Archaeologists have excavated agricultural features in the Basin of Mexico, including chinampas, drained fields, terraces, and canals to detail their chronology and function. (Evans, 1990; Morehart & Frederick, 2014; Nichols, 1988; Nichols & Frederick, 1993; Nichols et al., 2006; Parsons, 1976; Parsons et al., 1985). Ongoing land use, erosion, and deposition since 1521 present challenges. Micro- and macrobotanical analyses provide evidence of crops, but also vegetation, and environmental changes (McClung de Tapia & Martínez, 2017; Morehart & Eisenberg, 2010). McClung de Tapia (2015) and colleagues’ long-term, multimethod study of landscape change in the Teotihuacan Valley offers a model applicable not only elsewhere in the Mesoamerica, but to other world regions. Geoarchaeology has provided new details about pre-Hispanic farming and earlier landscape change (Cordóva & Parsons, 1997; Frederick, 2007; Smith et al., 2013). Advances in geophysics, multispectral aerial imagery, and new methodologies, along with historic aerial images, have aided detection of buried agricultural features such as canals. (Armillas, 1971; Luna, 2014; Morehart & Frederick, 2014; Nichols, 1988; Sanders et al., 1979). However the great expansion of Mexico City and surrounding cities and towns in the latter part of the 20th century also obscured and destroyed thousands of sites.

Ethnographic studies of farming practices in the early and mid-20th century before the widespread use of tractors, hybrids, etc., have also served as a basis for modeling pre-Hispanic land use practices (e.g., Luna, 2014; Sanders et al., 1979; Parsons & Parsons, 1990). Documentary sources on the Aztecs and their descendants, referred to as nahuas in the colonial period, offer a rich source of information (Kovar, 1970; Rojas, 1988; Smith, 2012, pp. 65–81). For example, the Florentine Codex (Sahagún, 1950-1982, Bk. 11, p. 252) describes different kinds of agricultural land, “Metalli, this earth spread with maguey plants; provided with maguey plants, with maguey roots. It is made replete with maguey plants. Atlalli. Its name is [so] called from atl {water} and tlalli [earth].” Williams and Harvey (1997)—see also Williams (1991)—undertook an important study of Aztec land tenure in Tepetlaoxoltoc in the eastern Basin of Mexico from the Códice de Santa María Asunción. The colonial period sources indicate that the major problems of agricultural adaptation were similar to those identified in ethnographic studies of farming practices (Kovar, 1970).

Documentary sources also aid understanding changes during the colonial period (Hassig, 1985). Forced relocations of indigenous communities into nucleated settlements, population loss from epidemic disease and colonialism, and the introduction of grazing animals led to widespread abandonment of Aztec terrace systems and massive sheet and gully erosion and degradation (Melville, 1994; Sanders & Evans, 2001). Ignorant of Aztec hydroengineering, the Spanish built a dam to control flooding in Mexico City that backed up water into the lower Teotihuacan valley and deposited meters of sediment that covered colonial period and Aztec constructions and agricultural features (Gamio, 1922, pp. 370–371). Landscapes were altered so much in some places that agricultural features once thought to be pre-Hispanic such as chinampas around the springs at Teotihuacan may in fact date to colonial times (McClung de Tapia, 2012a).

In late 20th century, government-led land reclamation projects introduced chisel plowing on hillsides to break up the tepetate (volcanic tuft) bed rock to improve farming along with reforestation programs that disturbed and destroyed sites, a majority dating to Aztec times (Parsons, 2015), but also some of the earliest villages. Rapid population growth and urbanization contributed to the destruction and building over of important pre-Hispanic irrigated areas—many of which had been continuously cultivated into the 20th century—making it difficult to detect surface pre-Hispanic features. Despite these challenges, important advances have been made in understanding pre-Hispanic agriculture.

The Setting

The Basin of Mexico is an internal drainage basin that encompasses 7,000 square km of the southern part of the Central Mexican plateau. The Basin floor lies at 2,240 m with sierras rising to 4,000 to 5,000 m. Rainfall follows a marked rainy and dry season; rains may begin in late spring and continue into the fall but the timing and amount of rainfall, mostly occurring in the form of intense thunderstorms, is highly variable from place to place and year to year. Rainfall is highest in the southwest Basin and lowest in the northeast Basin. Sanders et al. (1979) subdivided the region into topographic zones—they referred to the lower slopes suitable for agriculture as the piedmont, where rainfall tends to be higher than on the basin floor.

The Basin of Mexico lies in the tierra fría where intense frosts occur in winter, sometimes beginning as early as September. Above 2,700 m it was generally too cold for farming. Farmers had to contend with risks of late spring rains, and varying amounts and timing of rainfall during the growing season along with the risk of early fall frost. The frost risk is less in the lower and middle piedmont and along the lakeshore and rainfall is slightly higher on the hillslopes. Soils are generally shallow on the hillslopes and very prone to erosion. Recent paleoclimate models suggest an increase in rainfall that perhaps facilitated the regional population growth during the 13th and 14th centuries, but the climate model has yet to be fully tested (Smith, 2012, p. 60; Stahle et al., 2011).

McClung de Tapia (2015) provides an excellent overview of paleoenvironmental research in the Basin of Mexico. The Basin of Mexico was home to earlier large states and cities and farmers had been cultivating fields for thousands of years since 1500–1000 bc. Some of the most significant anthropogenic changes took place as a result of deforestation associated with early farming of hillslopes (Nichols, 2015) and then the growth of cities as documented at Teotihuacan in the northeast Basin by McClung de Tapia (2015). McClung de Tapia’s long-term paleoenvironmental studies offer an excellent model research design applicable elsewhere. In other places, population loss allowed soils to build up (Cordóva & Parsons, 1997; Frederick, 1997; McClung de Tapia, 2015, p. 381). Except for colonization of the upper piedmont, which had previously been unoccupied by farming villages, by 1100 ad most of the Basin of Mexico had been settled by farming populations for several thousand years (Sanders, 1981; Sanders et al., 1979).

Interconnected shallow lakes covered the Basin floor. The central portion of the lake system, Lake Texcoco, was saline while the southern lakes (Chalco-Xochimilco) were freshwater, and the northern lakes (Zumpango-Xaltocan) varied from saline to brackish. The lakes provided a valuable transportation artery within the Basin and lakeshore trade grew during the Middle and Late Postclassic. The lakes also were a rich resource for fish, birds, reeds, salt, and insects (Milhauser, 2017; Parsons, 2010). Mesoamerica was the only world region where primary states developed that had no domesticated herbivores for food, byproducts (e.g., wool, leather), dung for fuel, or transportation. How then did this region support large urban populations? Parsons (2010) argues that exploiting lacustrine resources, which became quite specialized in Aztec times, was one of the keys.

Crops

Maize was the staple crop of the Aztecs, their predecessors, and descendants and many varieties were bred and adapted to local conditions. The Aztecs ate maize in variety of ways. To make tortillas, they first soaked shelled maize in an alkali solution (usually water and limestone or ash), a method of preparation that increases the nutritional value of maize. They ground the wet kernels into dough on a grinding stone, metate, shaped the tortillas with their hands, and cooked them on a ceramic griddle, comalli. Maize dough also could be shaped into balls; filled with beans, chiles, or more rarely meat; wrapped in maize leaves; and steamed to make tamales. They made soup with larger kernels (in English called hominy) and also drank fine maize flour mixed with water and other flavorings as pozole. They sometimes enjoyed newly picked maize on the cob, called elote.

Beans were also standard fare. They were intercropped with maize and as legumes, beans have bacteria that introduced nitrogen into the soil system that helped compensate for nitrogen-demanding maize. Squash would also be interplanted with their maize stalk vines. At harvest, farmers removed the edible portions of plants, but turned back into the soil other parts of the plant; in a semiarid climate without animal dung for fertilizer, any source of organic matter for cultivated fields was important for productivity. Amaranth was another seed crop but there is less information about its cultivation. Most famously, amaranth dough was shaped into figurines of deities and eaten on ritual occasions. Chile peppers in a wide variety provided flavor, but also nutrition, as did herbs, tomatoes, and avocados.

More than any other region of primary civilization, in recent decades archaeological, ethnographic, and documentary research all point to the intensive cultivation of cacti as a largely overlooked but important complement to seed crops (Figure 3).

Agricultural Practices and Environmental Impacts of Aztec and Pre-Aztec Central MexicoClick to view larger

Figure 3. Maguey and nopal Plants, Altica, Teotihuacan Valley 2014.

Author’s photo.

Farming xerophytic plants had become a specialty of the northern Basin of Mexico (Blanton, 1996). Maguey, a member of the agave family, was an important multipurpose plant that grows well in the semiarid highlands (Parsons & Parsons, 1990). It provided an important source of food and its cultivation complemented and did not compete with seed crops. The plant produces both edible flesh and sap. Farmers induce sap production by interrupting the last stages in the plants maturation, which, depending on the variety and conditions, takes 7 to 25 years. When a maguey plant reaches maturation, farmers cut into its core/heart, scrape the plant each day, and siphon off the sap over a period of three to six months. The Aztec tool kit included distinctive scrapers made of obsidian for this purpose. In any particular field, a farmer will stagger planting magueys such that in any given year 5 to 10 percent of the plants produce sap, making 5,000–9,000 liters of sap in a year. The sap may be directly consumed, as aguamiel, or fermented to a mildly alcoholic beverage, pulque. Parsons (2010, p. 115) points out both are unstable and do not store for long periods, but can be boiled into sugar. People also cooked the heart, leaves, and stalk and even baked it for storage.

Another major use of maguey was for fibers. Cotton and maguey were the principle source of fibers—cotton did not grow in the Basin of Mexico. One of the first regions Teotihuacan and the later Triple Alliance gained control of outside the Basin of Mexico was semitropical Morelos where cotton flourishes. Cotton cloth was the most demanded item on Aztec tribute lists and served as a medium of exchange. Nearly every household spun fibers as indicated by the presence of ceramic spindle whorls. Pre-Hispanic people in Mesoamerica did not employ spinning wheels but rather a wooden spindle and perforated ceramic weight, a whorl. At Otumba, we found the first reported maguey processing workshop that also produced, spindle whorls, ground stone implements—the workshops were household based and located in a neighborhood in the craft manufacturing section of the town (Nichols et al., 2000). Complementary aspects of maguey processing and manufacturing were combined in these household workshops. Maguey cultivation for both fibers and food became a specialty of the northern Basin of Mexico at least as early as Teotihuacan and likely during the Formative period (Robertson & Cabrera, 2017). The use of mold-made ceramic whorls by the Aztecs standardized thread sizes, likely in response to markets and the role of cloth in tax payments. Maguey fibers were woven into clothing, but also used to make a variety of products, including sandals, string, ropes, and carrying bags.

Dried maguey stumps were also used and sold for fuel (Parsons, 2010, p. 119). Below the sierras, trees were sparse in Aztec times and analysis of grinding tools indicates that fuel was increasingly scarce in towns such as the Otumba in the northeast Basin of Mexico (Biskowski, 2000, p. 303). In addition to maguey, another cactus widely cultivated by Aztec farmers was nopal or prickly pear cactus. It produces a sweet, fleshy fruit that is an important cash crop in the northeastern Basin. The leaves with spines removed also provided a green vegetable. Cochineal, a valuable dye, was made from the dried bodies of insects that grow on nopal leaves. Colonial sources indicate that the northeastern Basin was a major producer and exporter of cochineal (Nichols, 2013). Unfortunately, maguey and other xerophytic plants do not preserve well in archaeological deposits so archaeologists have relied on tools used in processing maguey, ceramics, and ethnoarchaeology. Advances in residue studies provide a new methodology to understand the cultivation of maguey, nopal, and other xerophytic plants (Robertson et al., 2017).

Pre-Hispanic Land Use

Prehispanic farmers practiced various land use systems that depended on a variety of environmental and social factors, ecology, topography, soils, hydrology, climate, risk, soils, household and political economy, urbanization, and prior land use. Aztec farmers drew on knowledge and agricultural techniques developed over several thousand years but they also innovated and practiced intensive systems of land management on a greater scale than in any previous periods. By the end of the 1400s most arable land in the Basin of Mexico was under cultivation.

Rainfed Agriculture

Dry farming, temporal, or rainfed cultivation was practiced in the Basin of Mexico, both in deep soil areas of the Basin floor and on hillslopes. By the Late Postclassic period rainfed farming was relatively minor in the Basin of Mexico. Labor input was low, but productivity was highly variable. In the northern Basin rainfed farming was high risk, rather less so in the deep soil plains of the wetter southern Basin (Nichols, 1987). The earliest farming villages c. 1500 bc concentrated in the southern Basin where they also had access to the freshwater lakes. The process of agricultural villagers expanding into the driest northern portions of the Basin began c. 1000 bc and continued into Aztec times. The earliest farming villages in the northern Basin of Mexico, Tlaxcala, and Puebla settled on hillsides and practiced a highland form of swidden cultivation without terracing that triggered erosion (Nichols, 1982; see references in Nichols, 2015). With abundant land, early villages relocated. The earliest villages, even in the drier northern Basin of Mexico (as at Altica in the Teotihuacan Valley) already were embedded in systems of social differentiation, prestige competition, and sumptuary exchange being underwritten by surplus production and trade (Stoner et al., 2015). As early as 1000 bc farming practices caused anthropogenic landscape changes and, at least in the Ecatepec area of the Basin, this likely encouraged early floodwater irrigation of the valley floor (Nichols, 1982).

During the Late Postclassic population growth spurred the first substantial expansion of farming villages into the upper piedmont where only four-month varieties of maize will grow because it is too cold. Rainfed agriculture had to balance risks of late spring or early fall frost against the delayed onset of spring rains until late May or June, along with fluctuations in the amounts and timing or rainfall during the summer rainy season. Because cold air settles downslope, the lower piedmont has the lowest risk of frost except around the margins of the southern lakes, but soils on hillslopes that represent about 45 percent of the arable land in the Basin (Sanders et al., 1979, p. 225) were highly susceptible to erosion.

Terracing

Aztec farming households dramatically expanded agricultural terracing of piedmont hillslopes. The piedmont hillsides of the Basin of Mexico were once covered with remnants of Aztec terraces and houses where both maize and other seed crops were intensively cultivated along with maguey and nopal (Sanders et al., 1979, p. 251). Terracing made the fragile hillsides of the northern Basin of Mexico into productive agricultural lands and complemented farming of the irrigated deep soil plains. The use of terracing in pre-Aztec times is less well documented.

Aztec farmers built metepantlis, earthen terraces using rows of maguey and sometimes also rock and earth. The maguey rows catch colluvium and thus reduce erosion and also build up these soils for farming as well as house construction. Houses or clusters of houses were continuously dispersed. Most of these were contour terraces, but farmers also built check dams or cross-channel terraces (Donkin, 1979; Smith & Price, 1994). Agriculture terraces reduced erosion and allowed the buildup of soil to conserve moisture. They also provided a level surface for planting and house construction. In other parts of Central Mexico, farmers typically built stone terraces.

Terracing might also be combined with irrigation. Most often this involved floodwater irrigation where the fast-moving water following intense summer rainstorms was diverted onto fields using dams of earth, brush, rock, and sometimes masonry to direct water into canals that were simple earthen ditches. Trapping floodwaters following intense summer rainstorms concentrated water onto productive terraced fields and reduced erosion (Evans & Nichols, 2015; Nichols, 1982, 1988; Nichols et al., 1991, 2006; Sanders et al., 1979, pp. 253–255) describe how some large piedmont terrace complexes trapped runoff from steeper slopes above them in the Teotihuacan Valley. Dams were built across seasonal streams called barrancas to form a temporary pond; water was diverted into primary canals with temporary earth or earth and rock dams, and then distributed into secondary canals to water individual fields.

Michael Smith and his colleagues investigated one of the most elaborate terrace complexes of the Late Postclassic at the urban capital of Calixtlahuaca, a large city in the Toluca Valley (Smith et al., 2013). Despite the elaborate terracing and channels, they concluded that there and elsewhere terraces were built and maintained by households or neighborhoods—there is no evidence of central management. Key to this landesque intensification was the ongoing maintenance of the terraces. A breach through neglect or abandonment led to rapid erosion as happened on a massive scale under Spanish colonialism. Maintaining terraces and managing floodwaters favored the dispersed piedmont settlement pattern, a signature of Aztec agriculture on hillsides (Evans, 1998).

In some cases, terraces were constructed to reclaim previously cultivated and eroded lands. The popular view associates environmental degradation with population growth and overintensification. But population loss and abandonment also causes degradation. The growth of the huge city of Teotihuacan c. 100 bc was associated with increased erosion; as yet we have little evidence for Teotihuacan period terracing (McClung de Tapia, 2015). With most farmers living at Teotihuacan, later Postclassic terraces might obscure remains of earlier earthen terraces. Just as the growth of the city altered regional settlement patterns and agricultural land use, so did the collapse of the city c. ad 550–650. The retraction of the Teotihuacan period population in the Texcoco pediment set off erosion cycles and Cordóva and Parsons (1997) document how the land was reclaimed in Aztec times. The Teotihuacan period occupation at Cerro Portezuelo in the southeastern Basin of Mexico was completely obscured by soil eroded from the higher slopes at the end of the Early Classic period (Nichols et al., 2013).

Irrigation

The technology and organization of most pre-Hispanic irrigation systems in the Basin of Mexico was simple. These were gravity flow systems where water was moved from the source through canals, usually earthen ditches, dug into the upper soil strata or tepetate bedrock on hillsides. Storing irrigation water for later use has not been documented as a significant practice. Irrigation supplemented rainfall to water fields in the spring before the onset of the summer rains and allowed earlier planting and watering during the growing season. Thus, most of the water for crops came from rainfall, but irrigation was critical to reduce risk and achieve more consistent crop yields with less variability from year to year and place to place (Nichols, 1987).

The types of pre-Hispanic irrigation are distinguished by the nature of the water supply. Permanent irrigation systems drew water from perennial rivers and springs. Sources of water for permanent irrigation were restricted in the Basin of Mexico. By the early 16th century, Aztec farmers were using all the permanent water sources for irrigation, including (a) Teotihuacan where the largest concentration of springs was located; (b) above Texcoco at the juncture of the piedmont and sierras in the eastern Basin of Mexico; (c) along the lakeside edge of Chimalhuacan; (d) the Cuauhtitlan and Tepotztlan rivers in the northwest Basin; (e) springs above Coyoacan on the southern shore of Lake Texcoco; and (f) springs along the southern edge of Lake Chalco-Xochimilco. The Cuauhtitlan and Teotihuacan systems irrigated their alluvial plains on the Basin floor. The Texcoco and Coyoacan systems irrigated fields both on piedmont slopes and alluvial plain. The springs along the southern lakes helped regulate water levels for chinampas (Nichols & Frederick, 1993; Nichols et al., 2006; Sanders et al., 1979, p. 76). All the permanent irrigation networks irrigated fields belonging to multiple communities and thus entailed some degree of intercommunity cooperation. Permanent sources of water allowed preplanting irrigation to begin as early as late winter—even if planting was not done until spring, crops could begin to grow from the subsoil moisture. A final irrigation might have been done in the fall to moisten the soil for the following spring planting.

Permanent irrigation systems involved large-scale public works. The Cuauhtitlan Valley in the northwestern Basin comprised the largest drainage in the Basin of Mexico. In the 1400s, the ruler of the city-state or altepetl of Cuauhtitlan directed the rerouting of the Cuauhtitlan river that required seven years to finish and involved building an irrigation network northwest of the town (Doolittle, 1990, pp. 118–119). This created the largest irrigation system in the Basin with the potential to irrigate 8,000 to 10,000 ha. (Nichols & Frederick, 1993, p. 135). Cuauhtitlan also became one of the largest Late Postclassic tributary confederations in the Basin of Mexico as through wars and alliances it ruled all the irrigated lands. Diverting the Cuauhtitlan River might also have contributed to the abandonment of Xaltocan’s (a long-standing rival city-state) chinampas (Morehart & Frederick, 2014). At Teotihuacan, c. ad 100 rivers and even seasonal streams were rerouted to conform to the city’s grid (Evans & Nichols, 2015). Detecting subsurface pre-Hispanic permanent irrigation features on alluvial plains has proven a difficult problem because of deposition and urban buildup in some areas, or because of continued use in other areas such as the Teotihuacan Valley.

Where permanent irrigation was not available floodwater irrigation watered fields on deep soil alluvial plains and piedmont terraces. Floodwater irrigation features have been studied the most by archaeologists in the Teotihuacan Valley where it was widely practiced by 100 bc (Nichols, 1988, 2015; Nichols et al., 1991, 2006; Sanders & Evans, 2001) (Figure 4).

Agricultural Practices and Environmental Impacts of Aztec and Pre-Aztec Central MexicoClick to view larger

Figure 4. Teotihuacan Period canal excavation, Tlajinga.

Author’s photo.

Farmers built dams of earth, stone, or masonry across barrancas at points where the streambed was relatively shallow. After a high-intensity rainstorm, surface runoff flowed into the stream where it was blocked by a dam and created a temporary pond. The dammed water was then directed into primary canals. Temporary brush diversionary structures were built across secondary canals to divert water onto fields. These dam-canal complexes were usually small, and irrigated at most 50 to 100 ha. A major barranca might have multiple complexes. On piedmont hillslopes floodwater irrigation was combined with terracing. Controlling the flow of runoff water on hillslopes was critical, as too much runoff at a high rate would damage crops. Formal water regulation was not a feature of floodwater systems managed by local households. Erosion and sedimentation were ongoing aspects of floodwater irrigation that intensified under Spanish colonialism.

Irrigation water, both from floodwaters and from permanent sources, also supplied fresh soil material to fields. This was especially valuable for maintaining soil productivity in pre-Hispanic times because manure from large animals was lacking. Aztec systems of land classification mention different kinds of fertilized land, including old house sites, fertilizing with wood, and land fertilized by incorporating vegetation into the soil (Sahagún, 1950–1982, Bk 11, pp. 210–212). Night soil was collected in Tenochtitlan for use as fertilizer (Diaz, 1927, p. 177).

A long-term program of household archaeology at Xaltocan begun by Elizabeth Brumfiel (Brumfiel, 2005) and continued by her former students revealed new fine-grained details of Aztec agricultural intensification. Morphological changes in maize identified by Morehart (2014; Morehart & Eisenberg, 2010) point to its more intensified use. This is consistent with DeLucia’s (2013) findings of intensified maize use based on microarchaeology of Xaltocan households—an approach that warrants wider application.

Chinampas

The most famous and most dramatic agricultural system was the Aztec expansion of chinampa farming in the southern lakes of the Basin of Mexico, and around Xaltocan in the north (Figure 5).

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Figure 5. Chinampas, San Gregorio Atlapulco, Mexico, 1980.

Photo taken by Jeffrey R. Parsons.

Chinampas are a form of drained field agriculture where, in contrast to irrigation, too much water poses problems (Morehart, 2017). Farmers built the fields by digging canals through the swampy lands of the lakes and piling up muck and decayed vegetation to form islands between canals. Chinampas are among the most productive preindustrial farming systems as they could be continuously cultivated. Chinampa farming on a small scale might have begun in the Formative period (Nichols, 2015). Both Sanders et al. (1979, p. 269) and Scarborough (2003) argue that the development of chinampas in the swampy area around the springs at Teotihuacan were critical in the growth of the city, but no drained fields have been dated to Teotihuacan times (McClung de Tapia, 2012a, p. 153).

The narrow Aztec chinampas could be kept in continuous production because of fresh soil and nutrients from the muck and decayed vegetation deposited on fields, the use of seed beds, and regulation of water levels that also provided protection from frost, as well as drought (Luna, 2014). The chinampas in the city of Tenochtitlan were residential, although people cultivated gardens. According to Calnek (1972), no farmers resided in the imperial capital by the start of the 16th century.

Construction of Xaltocan’s chinampa system in the northwestern Basin of Mexico began during the Early Postclassic and represents the only conclusively dated pre-Aztec chinampas. Xaltocan was the island capital of an important Postclassic city-state surrounded by Lake Xaltocan. Morehart and Frederick (2014) conservatively estimated the system encompassed 1,500 to 2,000 ha. Primary canals carried freshwater from springs to the brackish lake water and also were used for transportation. Secondary canals distributed the water from the primary canals to tertiary canals that separated individual fields. The chinampas were organized into groups or parcels of individual fields and suprahousehold organization was required for the Xaltocan system to function and regulate the supply of freshwater. Unlike intensive agricultural systems elsewhere in the Basin that reached their maximal extent during the Late Postclassic, Xaltocan’s chinampas were abandoned. Morehart and Frederick (2014) link their abandonment in the 1400s to Xaltocan’s defeat first by Cuauhtitlan and then the Mexica and loss of its political autonomy. Cuauhtitlan’s diversion of the Cuauhtitlan river might also have disrupted the flow of freshwater to the chinampas.

The Aztecs converted about 12,000 ha of marsh of the southern freshwater lakes into chinampas. To control both the amount of water and its salinity required regulating the level of water between Lakes Chalco, Xochimilco, Texcoco, Xaltocan, and Zumpango. This was accomplished through a complex of canals, dikes, and sluice gates that had to be coordinated through, “system-wide control of water levels [which] was vital for constructing and cultivating raised fields throughout the southern lakes” (Luna, 2014, p. 54). Royal engineers also had to protect Tenochtitlan from flooding when lake levels rose. Luna’s important recent study revealed unexpected findings. He discovered that a much larger number of people lived on the Chalco-Xochimilco lakebed. This increased his estimate for the productivity and size of the southern chinampa zone, closer to 15,000 ha compared to 12,000 ha of previous estimates, enough to produce surplus grain to feed 50,000 people. Luna found that the narrowness of Aztec chinampas, 3.75 m wide, was critical to their sustainability; it regulated their temperature for frost protection; replaced nutrients with lake muck, water, and vegetation; and made it possible to water individual plants by hand splashing or by pouring using containers to collect water from their canoes. He argues that imperial management was critical in the expansion and operation of the southern chinampas away from the islands and shoreline; consequently, the defeat of the Triple Alliance quickly led to the collapse of Aztec management and rapid inundation by lake waters and a return to marshes. (Luna, 2014, p. 178). Until then the nearness of the southern chinampas zone and resulting ability to transport bulk food crops to Tenochtitlan by canoe further enhanced their economic importance.

The great expansion of chinampas in the southern lakes in the 1400s made them the “breadbasket” for the expanding city of Tenochtitlan where canoe transportation through canals and across the lake facilitated provisioning the city and its markets. Although chinampa construction was not as regular as once assumed (Frederick, 2007), top-down management of the southern chinampas likely was an element of some aspect of the rapid expansion. Luna (2014, p. 54) emphasizes that the southern chinampas depended on system-wide control of water levels of the southern lakes. Too much water posed a serious threat. Royal imperial engineers managed water levels while construction of raised fields likely was done by individual households and local communities. Both Parsons et al. (1985) and Luna concluded that the rapidity of the chinampas expansion, the amount of construction, and the labor involved required some central administration. Parsons et al. (1985) proposed that this was accomplished by relocating tenant farmers, perhaps people who had lost land in wars of conquest, to augment the locally available labor.

Aztec Gardens

Susan Evans’ (2017) study of royal gardens, parks, and pleasure palaces shows how agriculture was embedded in hierarchies of power and wealth. Her research has drawn attention to their importance. The famed Acolhua ruler Nezahualcoyotl’s park at Texcotzingo is among the most famous examples (Wolf & Palerm, 1955). Its eight-kilometer long aqueduct carried water from the sacred mountains to supply fountains and baths and irrigate fields below. He brought exotic plants and animals to create lush gardens in the park that were dedicated to Tlaloc the Aztec deity linked to rain. Evans points out that the Aztecs also devoted royal parks and gardens to botanical study. The royal parks and gardens expressed the wealth and power accrued by its rulers (Evans, 2017).

Theoretical Considerations

The early comparative perspective of Julian Steward (1955), his method of cultural ecology and neoevolutionism, and the influence of Pedro Armillas after WWII drew early attention to the Basin of Mexico as an important region to test ideas about the role of irrigation in the development of states. Armillas (1971), Millon (1957), Palerm (1955, 1961), Sanders et al. (1979), and Wolf and Palerm (1955) sought to establish that irrigation and chinampas’ drained field agriculture were important to the Aztec economy. Although controversial, Wittfogel’s (1957) hydraulic theory stimulated problem-oriented research in both archaeology and ethnography in the Basin of Mexico (see Nichols, 2015, and the overview in Sanders et al., 1979). Sanders (Sanders et al., 1979, p. 5) envisioned the Basin of Mexico settlement pattern program as an explicit test of the method of cultural ecology and multilinear evolution to consider the relationship between settlement patterns, agricultural land use, and population in the evolution of civilization. He saw ecological diversity as another driving force in agricultural intensification.

Scholars soon divided, however, on the role of hydraulic agriculture in political centralization. Millon concluded that pre-Hispanic irrigation, at least at Teotihuacan, was not centrally managed (Millon & Altschul, 2015). Sanders (1981), on the other hand, saw large-scale hydraulic agriculture as a source of power. At same time, he also embraced the ideas of agricultural economist Esther Bosserup (1965). She made the case for understanding intensification as a process—working in tropical Africa she saw intensification as driven by population pressure and land availability. Sanders and colleagues pointed to risk in the Basin of Mexico as also important (Nichols, 1987; Sanders & Webster, 1978). At the same time, they and others were influenced by the work of Jane Jacobs in cities, and economic geographers on how urbanization encouraged intensification. Sanders and Santley (1983) drew on Tenochtitlan, Tula, and Teotihuacan as examples.

Beginning in the mid-1970s, population pressure and other prime mover models were critiqued (Cowgill, 1975; Offner, 1981). Brumfiel (1992), incorporating developments in social theory, argued in favor of agency approaches and away from ecosystems frameworks. Based on her research at the Aztec city-state center of Huexotla in the eastern Basin of Mexico, she argued that the growth of Tenochtitlan as an imperial capital reoriented the economies of the city-states in the core of the Basin of Mexico to intensify agricultural production to supply urban demands (see also Hassig, 1985). These debates prompted a series of research projects at Aztec provincial capitals and rural sites (see Nichols & Evans, 2009; Nichols & Rodríguez-Alegría, 2017; Smith, 2012) that included investigations of Aztec chinampas, irrigation, and terraces. The importance of maguey cultivation and exploiting lacustrine resources and how they complemented seed crops is now generally recognized.

Household archaeology also shifted the focus away from top-down theories of culture change to consider strategies of households, as in Hirth’s (2009) Housework volume. Political economy became an important framework. Blanton et al.’s (1996) dual process theory was highly influential. These sources drew attention to how, in the same region, political economy strategies would shift from corporate to exclusionary and the Basin of Mexico was one of their case studies. In Mesoamerica, corporate strategies were associated with large-scale irrigation of alluvial plains, as in the Basin of Mexico.

A major reconceptualization of ancient economics has taken place (Nichols et al., 2017). Archaeologists and ethnohistorians documented the importance of Aztec commerce and markets and directly challenged the once widely influential ideas of Karl Polanyi. The growth of Aztec commerce and fiscal structures (taxes and tribute) also catalyzed agricultural intensification and specialization. The Triple Alliance tax system took into account economic factors, transportation costs, and ecology—staple foods were rarely demanded as tax payment beyond the distance of a five-day walk from Tenochtitlan (Berdan & Smith, 1996). Regional specializations such as cacao and cotton production increased.

The general theoretical diversification of Mesoamerican archeology (Nichols & Pool, 2012) that began in the late 20th century certainly applies to understanding pre-Hispanic agriculture with different scholars variably weighting economic, political, social (e.g., gender), and ideological factors. McClung de Tapia (2012b; McClung de Tapia & Martínez, 2017) advocated replacing cultural ecology with historical ecology as a more productive approach to the long-term recursive relationship between environment and society. Archaeology and environmental history are compatible allies with historical ecology, although cultural ecology continues to have proponents (Evans, 2013). Political ecology has entered the discussion to consider how political power shaped the agricultural landscape (Evans & Nichols, 2015; Morehart, 2017). Morehart discusses how a considerable commitment in landesque agricultural capital, terraces, chinampas, and irrigation bound farmers to place, thus making them vulnerable to exploitation and manipulation by local lords and imperial powers. The Teotihuacan and Aztec states were involved in major hydraulic projects (Doolittle, 1990; Luna, 2014; Palerm, 1973; Scarborough, 2003, 2012) but most pre-Hispanic agriculture did not require direct state administration. In fact, such is best left in the hands of farmers and their local communities. Through taxes and tribute the hierarchy of power in the Aztec empire and earlier states effected agriculture more subtly than Wittfogel’s despots (Morehart, 2017; Nichols et al., 2017; Offner, 1981). By Teotihuacan times farmers were also engaged in commerce; they sold crops and prepared foods in markets where they obtained household goods, and commerce intensified during the Postclassic to the point that cacao seeds and cotton mantles were used as a medium of exchange by the Aztecs.

One of the most influential of recent approaches is collective action. Blanton and Fargher’s (2008) book is among the best in comparative research by archaeologists of the early 21st century. This brings us back to the question of hydraulic agriculture and political centralization. Elinor Ostrom (and Steve Lansing, 2006) showed how large, complex hydraulic system can develop and be managed without central administration. Vernon Scarborough (2003) argues that direct state intervention in the Basin of Mexico was situational (see also Carballo, 2013; Nichols, 2015). Luna’s (2014) new research on the southern chinampas indicates that construction was largely in local hands, but regulating lake levels required more centralized management. This warrants further theoretical consideration and empirical research.

The Aztecs and their predecessors had a deep practical knowledge of their environment, crops, and farming systems. As everyone in the 16th-century world, they understood cosmology and cosmogenesis within a framework of ultimate sacred powers and propositions. People had a reciprocal relationship with those powers that they fulfilled through ceremonies, rituals, and offerings. McClung de Tapia and Martínez (2017) suggest that chinampas especially expressed this relationship. Farmers created lands in the sacred waters of the lake where previously no land existed. Their need to obtain sustenance from this consecrated landscape was embedded within a complex ritual cycle that mitigated the potential imbalance in the cosmic equilibrium that such exploitation might provoke (2017, p. 182). Crops from these fields sustained the ritual cycle by providing offerings of food and flowers, and nourishing people whose blood was the ultimate debt payment.

Concluding Thoughts

The other important contribution of research about pre-Hispanic agriculture in the Basin of Mexico is its historical perspective. Agricultural intensification changed the physical landscape of the Basin of Mexico in small and dramatic ways that supported the growth of large cities and imperial states. We also can point to effects of erosion, deposition, vegetation loss, and short- and long-term climate changes. The so-called Columbian exchange, however, resulted in greater degradation than any so far documented in the pre-Hispanic era. The loss of population, introduction of grazing animals, and forced resettlement of dispersed hillside villages into nucleated towns precipitated massive sheet and gully erosion (Melville, 1994). Spanish ignorance of Aztec engineering and farming systems led to the collapse of the southern chinampas zone. The Basin of Mexico provides a compelling rejection of “the pristine myth in the Americas” and the premise that the Anthropocene began with the Industrial Revolution. The encounter between the Spanish and Aztecs/Nahuas played out in a landscape of Central Mexico that itself had been shaped for over a millennium by intensive agriculture, large populations, cities, and empires. Nahua farmers also adapted to changing conditions, new crops, and new markets, and contributed to the spread of one of world’s great culinary traditions and its Nahuatl names.

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                                                                                                                                                                      Sanders, W. T. (1981). Ecological adaptation in the Basin of Mexico: 23,000 B.C. to Present. In J. M. Sabloff (Ed.), Archaeology Supplement to the Handbook of Middle American Indians (pp. 147–197). Austin: University of Texas Press.Find this resource:

                                                                                                                                                                        Sanders, W. T., & Santley, R. S. (1983). A Tale of Three Cities: Energetics and Urbanization in Pre-Hispanic Central Mexico. In Evon Z. Vogt & Richard M. Leventhal (Eds.), Prehistoric Settlement Patterns: Essays in Honor of Gordon R. Willey (pp. 243–291). Albuquerque and Cambridge, MA: University of New Mexico Press and Peabody Museum of Archaeology and Ethnology, Harvard.Find this resource:

                                                                                                                                                                          Sanders, W. T., & Evans, S. T. (Eds.). (2001). Teotihuacan Valley Project, V. 5 Pt. 3: The Aztec Period occupation of the Valley, syntheses and general bibliography. Occasional Papers in Anthropology. University Park: Department of Anthropology, Pennsylvania State University.Find this resource:

                                                                                                                                                                            Sanders, W. T., Parsons, J. R., & Santley, R. S. (1979). The Basin of Mexico: Ecological processes in the evolution of a civilization. New York: Academic Press.Find this resource:

                                                                                                                                                                              Sanders, W. T., & Webster, D. (1978). Unilinealism, multilinealism, and the evolution of complex societies. In Redman, C. et al. (Eds.), Social archaeology: Beyond subsistence and dating (pp. 249–302). New York: Academic Press.Find this resource:

                                                                                                                                                                                Scarborough, V. L. (2003). The flow of power: Ancient water systems and landscapes. Santa Fe, NM: School of American Research.Find this resource:

                                                                                                                                                                                  Scarborough, V. L. (2012). Agricultural land use and intensification. In D. L. Nichols & C. A. Pool (Eds.), Oxford Handbook of Mesoamerican Archaeology (pp. 542–551). New York: Oxford University Press.Find this resource:

                                                                                                                                                                                    Smith, M. E. (2008). Aztec city-state capitals. Gainesville: University Press of Florida.Find this resource:

                                                                                                                                                                                      Smith, M. E. (2012). The Aztecs (3d ed.). Oxford: Basil Blackwell.Find this resource:

                                                                                                                                                                                        Smith, M. E. (2017). Aztec urbanism: Cities and towns. In D. L. Nichols & E. Rodríguez-Alegría (Eds.), Oxford Handbook of the Aztecs (pp. 219–228). New York: Oxford University Press.Find this resource:

                                                                                                                                                                                          Smith, M. E., Borejasza, A., Huster, A., Frederick, C. D., López, I. R., & Heath-Smith, C. (2013). Aztec Period houses and terraces at Calixtlahuaca: The changing morphology of a Mesoamerican hilltop center. Journal of Field Archaeology, 38, 227–243.Find this resource:

                                                                                                                                                                                            Smith, M. E. M., & Price, T. J. (1994). Aztec period terraces in Morelos, Mexico: Evidence for household-level agricultural intensification. Journal of Field Archaeology, 21, 169–179.Find this resource:

                                                                                                                                                                                              Stahle, D. W., Villanueva, J., Burnette, D. J., Cerano, J., Heim Jr., R. R., Fye, F. K., . . . Stahle, D. K. (2011). Major Mesoamerican droughts of the past millennium. Geophysical Research Letters, 38(5), L05703.Find this resource:

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                                                                                                                                                                                                  Stoner, W., Nichols, D. L., Alex, B., & Crider, D. (2015) The emergence of Early-Middle Formative exchange patterns in Mesoamerica: A view from Altica in the Teotihuacan Valley. Journal of Anthropological Archaeology, 39, 19–35.Find this resource:

                                                                                                                                                                                                    Williams, B. J. (1991). The lands and political organization of a rural Tlaxilacali in Tepetlaoztoc, c. A.D. 1540. In H. R. Harvey (Ed.), Land and politics in the Valley of Mexico: A two-thousand year perspective (pp. 187–208). Albuquerque: University of New Mexico Press.Find this resource:

                                                                                                                                                                                                      Williams, B. J., & Harvey, H. R. (1997). Códice de Santa Mária Asuncíon: Facsimile and commentary: Households and Lands in Sixteenth-Century Tepetlazoaltoc. Salt Lake City: University of Utah Press.Find this resource:

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                                                                                                                                                                                                            Suggested Readings

                                                                                                                                                                                                            Berdan, F. F. (2005). The Aztecs and Central Mexico (2d ed.). Belmont, CA: Thomas Wadsworth.Find this resource:

                                                                                                                                                                                                              Berdan, F. F. (2014). Aztec archaeology and ethnohistory. Cambridge, U.K.: Cambridge University Press.Find this resource:

                                                                                                                                                                                                                Blanton, R. E., & Fargher, L. F. (2008). Collective action in the formation of pre-modern states. New York: Springer.Find this resource:

                                                                                                                                                                                                                  Evans, S. T. (2013). Ancient Mexico & Central America: Archaeology and culture history. New York: Thames and Hudson.Find this resource:

                                                                                                                                                                                                                    Frederick, C. (2007). Chinampa cultivation in the Basin of Mexico: Observations on the evolution of form and function. In T. L. Thurston & C. T. Fisher (Eds.), Seeking a richer harvest: The archaeology of subsistence intensification, innovation, and change (pp. 107–124). New York: Springer.Find this resource:

                                                                                                                                                                                                                      Luna, G. G. G. (2014). Modeling the Aztec agricultural waterscape of Lake Xochimilco: A GIS analysis of lakebed chinampas and settlement (Doctoral dissertation) Department of Anthropology, Pennsylvania State University, University Park. Retrieved from http://www.academia.edu/7738339/Modeling_the_Aztec_Agricultural_Waterscape_of_Lake_Xochimilco_A_GIS_Analysis_of_Lakebed_Chinampas_and_Settlement.Find this resource:

                                                                                                                                                                                                                        McClung de Tapia, E. (2012a). Silent hazards, invisible risks: Pre-Hispanic erosion in the Teotihuacan Valley, Central Mexico. In J. Cooper & P. Sheets (Eds.), Surviving sudden environmental change: Answers from archaeology (pp. 143–166). Boulder: University Press of Colorado.Find this resource:

                                                                                                                                                                                                                          McClung de Tapia, E. (2012b). Ecological approaches to archaeological research in Central Mexico: New directions. In D. L. Nichols & C. A. Pool (Eds.), Oxford Handbook of Mesoamerican Archaeology (pp. 567–578). New York: Oxford University Press.Find this resource:

                                                                                                                                                                                                                            McClung de Tapia, E. (2015). Holocene paeloenvironment and pre-Hispanic landscape evolution in the Basin of Mexico. Ancient Mesoamerica, 26, 375–389.Find this resource:

                                                                                                                                                                                                                              Morehart, C. (2017). Aztec agricultural strategies: Intensification, landesque capital, and the sociopolitics of production. In D. L. Nichols & E. Rodríguez-Alegría (Eds.), Oxford Handbook of the Aztecs (pp. 260–280). New York: Oxford University Press.Find this resource:

                                                                                                                                                                                                                                Parsons, J. R. (2010). The pastoral niche in pre-Hispanic Mesoamerica. In J. E. Staller & M. Carrasco (Eds.), Pre-Columbian foodways: Interdisciplinary approaches to food, culture, and markets in Ancient Mesoamerica (pp. 109–136). New York: Springer.Find this resource:

                                                                                                                                                                                                                                  Sanders, W. T., Parsons, J. R., & Santley, R. (1979). The Basin of Mexico: Ecological processes in the evolution of a civilization. New York: Academic Press.Find this resource:

                                                                                                                                                                                                                                    Scarborough, V. L. (2012). Agricultural land use and intensification. In D. L. Nichols & C. A. Pool (Eds.), Oxford Handbook of Mesoamerican Archaeology (pp. 542–551). New York: Oxford University Press.Find this resource:

                                                                                                                                                                                                                                      Smith, M. E. (2012). The Aztecs. (3d ed.). Oxford: Basil Blackwell.Find this resource: