Water and the Aztec Landscape in the Valley of Mexico

The Valley of Mexico has been home to two of the world’s largest cities. In the fifteenth and early sixteenth centuries, the Aztecs ruled much of Mexico from their island capital of Tenochtitlan; today, spreading over the ruins of that same city is Mexico City, a city of some 25 million people. The rise of Tenochtitlan in the fourteenth century depended upon an ecological miracle, the manipulation of a salty inland sea to create large zones of freshwater lakes and irrigated fields, whose crops sustained the peoples who lived in the many cities and towns of the Valley. The large inland sea that once dominated the Valley stretched some 60 kilometers from north to south - a connected system of five shallow bodies of water that were called lakes, but differed from true lakes in that they had no natural outlets to the sea (pic 1). These lakes swelled during the rainy season (June through October) with water coming in from rivers, streams and rainwater; evaporation into the air and absorption into the ground allowed the waters to recede. On the map, they appear as an enormous unified system, but there were significant differences between them.

Pic 1: Map of the Valley of Mexico, circa 1492

But their fertility was a fragile state: the three lakes that lay to the north, Tetzcoco, Xaltocan and Zumpango, were salty, and if saltwater washed into the southern lakes during floods, it would kill plants and ruin soil. Thus, the peoples of the southern lakes joined together to create a short (about three kilometer) dike and causeway (or raised road that functioned as a dike) across a natural bottleneck in the lake system. This so-called dike of Mexicaltzinco ran from the flanks of Huixachtitlan (Hill of the Star) near Culhuacan to Huitzilopochco (now called Churubusco), thereby sealing off and protecting their sweet water system.

Pic 3: Artist’s impression of the landscape surrounding Tenochtitlan: the dike of Mexicaltzinco can be seen bottom left

By the time the Spaniard conquistadors arrived in 1519, the edges of Chalco and Xochimilco were filled by kilometer upon kilometer of these “floating gardens,” and Spanish soldiers like Bernal Diáz del Castillo would later write about these “large maize plantations lying near the lake.” Some chinampas still exist today, to the south of Mexico City.

Because of chinampa agriculture, the southern lakes became the breadbasket of the larger Valley, supplying their northern neighbors around the lakes of Tetzcoco, Zumpango and Xaltocan with fresh vegetables, squashes, chiles, and corn throughout the year.

Pic 5: Model of chinampa agriculture, National Museum of Anthropology, Mexico City

Seeing the Chalco miracle, Moteuczoma attempted to create freshwater zones around his island city, so they could also have chinampas. This would seem, on the surface, impossible, since Tenochtitlan sat within the salty lake of Tetzcoco. But residents undoubtedly noted a natural phenomenon that occurred in the lakes. Because freshwater streams and springs flowed into the lake of Tetzcoco from the western side of the Valley, the water in the western part of the lake was relatively sweet, growing progressively more salty toward the east. But during the rainy season, salty water rushing into the lake of Tetzcoco from Lake Zumpango and Xaltocan would turn the whole system salty again.

Pic 7: Part of the remaining chinampa network at Xochimilco today

The first was the longest, running some seventeen kilometers north-south though the Lake of Tetzcoco. It was probably built in the mid-fifteenth century and called the dike of Nezahualcoyotl for the Tetzcocan king who engineered it. The second dike offered added protection. It ran within the area protected by the dike of Nezahualcoyotl to link the causeway of Tlalpan to the south to the causeway of Tepeyacac to the north with a stone wall that ran along the eastern edge of Tenochtitlan. It was called the dike of Ahuitzotl for the Aztec emperor who commissioned it around 1498-99.

Pic 9: Monument believed to commemorate the dike of Ahuítzotl, National Museum of Anthropology, Mexico City

The creation of these waterworks was a feat of ancient engineering akin to the construction of the great pyramids of Egypt. They relied on subtle differences in environmental conditions - like the flow of freshwater into the system, and the slightly higher elevations of the southern lakes and the western shores, which meant that water flowed from south to north and west to east. The peoples of the Valley were used to living with the water and used it to their advantage. In order not to impede the west-to-east flow of water in the Laguna of Mexico, the Mexica ran canals that ran west to east through their city; these proved useful for transport through the growing metropolis. Such a system of dikes and canals required constant maintenance and upgrading. Work on cleaning and maintaining the system was part of the labor obligation - a kind of tax paid by working--of many towns in the Valley.

Pic 11: Artist’s impression of Tenochtitlan and surrounding moonlit landscape

These raised causeways had breaks allowing the lake water to flow under them, spanned by bridges. At these breaks, the precious freshwater was carried across via great hollowed-out logs that spanned from one side of the canal to the other. At certain points where the water crossed a gap on these log bridges, the water sellers could gather in their canoes on the canal beneath and fill their large ceramic water jugs, and then take the canal route to the city’s markets or for home delivery.
Because travel by water is faster and more efficient than travel by road, canoes moved most of the goods through the Valley. Some of these were quite large, and Bernal Diáz wrote of canoes that were “hollow troughs cleverly cut out from huge single logs, and many of them would hold forty Indians.”

Pic 13: Artist’s impression of water-carrying by canoe; archaeological remains of a Mexica canoe (below) and of a model canoe (top right), National Museum of Anthropology, Mexico City

The great lakes of Mexico were turned into a battleground during the Spanish conquest of the Valley in 1519-1521. Spaniards, and their indigenous allies, built great warships to attack Tenochtitlan by water, and they smashed the aqueducts of Chapultepec and Nonohualco, depriving the city’s residents (there were perhaps 150,000) of the life giving water during the agonizing siege of the spring and summer of 1521. Victory declared, the conquistadores, many of whom were from bone-dry regions of Extremadura in Spain, paid little attention to the careful co-existence with water that peoples of the Valley had cultivated for generations.

Pic 15: The battle of Nonoalco, Florentine Codex, Book XII

The great project of the “desagüe” was successful in that by the early 20th century most of the lakes were gone, subterranean pumps working night and day to pipe water out of the Valley via tubes that cut through mountains. Today, Mexico City suffers from both chronic flooding and a shortage of freshwater; the problems once solved by the great engineers of the ancient Aztecs are at hand again.

Pic 17: Smog hovering over Mexico City today