By Julie Etra
Tenochtitlán was the capital of the Triple Aztec Alliance empire (formed in 1428 and ruled by the Mexica, the empire joined together the three Nahua states of Tenochtitlán, Texcoco, and Tlacopan). There is not enough space in this column to write about all the marvels of the Tenotchtilán itself, a magnificent city built on the five inland lakes in the Valley of Mexico. The Aztec empire was at its peak when Tenochtitlán was substantially destroyed by the Spanish Conquest in 1521.
Two of the most intriguing aspects of this civilization were its systems of agriculture/food cultivation and water management (they are of course intertwined), especially how these systems were constructed. For those readers interested in more detail, Barbara Mundy’s exhaustively researched and superbly written book is referenced below.
The Valley of Mexico
The basin that comprised the Valley of Mexico had five lakes: Zumpango, Xaltocan, Texcoco, Xochimilco, and Chalco. They were endorheic, i.e., they had no outlet, were hydraulically connected, and formed one enormous lake when flooded. The lakes were shallow, with a depth of no more than 150 ft (45 m); water quality varied. The more isolated southern lakes of Xochimilco and Chalco were higher and protected by the high peninsula formed by Cerro de la Estrella on the east and a “lava plug” to the west; the lakes were fed by springs and rivers, and so held fresh water. Drainage from the higher lakes flowed north to Texcoco (the largest lake), Zumpango, and Xaltocan; the waters of these lakes were brackish (saltier).
Following the discovery of a freshwater spring in Lake Texcoco at what came to be called Chapultepec (“grasshopper hill” in Nahuatl – chapulin = grasshopper, tepec = place), the rocky island of Tenochtitlán was settled on June 20, 1325. The brackish waters supported salt-tolerant aquatic life and were harvested for a species of algae made into edible patties. Flooding during the rainy season not only joined the lakes, but the backwash could threaten the innovative Aztec agricultural system known as chinampas.
The chinampas were rectangular gardens located in the southern lakes. Swampy land was dredged, creating navigable channels between islands. These islands were constructed with logs, reeds, and sticks woven into frames and covered with the muck of soil, mud, roots, and other dredged plant detritus. Whether or not these farmed rectangular parcels floated, as do the modern Floating Gardens of Xochimilco, is still subject to scholarly debate, although the establishment of willows would anchor them. While more investigation might reveal the actual materials, I would guess that the “reeds” included species of cattails (Typha spp.), bullrush (Scirpus spp.), and reeds (Cyperus spp.), all of which grow in standing water or saturated soils and are supple enough to weave. Ahuejote (Salix bonplandiana), an erect willow resembling a poplar, grew on the drier shores, along with ahuehuete (Taxodium mucronatum), aka sabino and Montezuma bald cypress. Ahuejote is derived from the Nahuatl word ahuexotl (atl = water, huexotl = willow). The Spanish word for willow is sauce; think of Sausalito, California, near San Francisco, meaning little grove of willows.
Young, flexible branches of willows were used in constructing the chinampas, and live cuttings were planted for eventual shade and to stabilize the structures through their vigorous and extensive root systems. (The bark of this versatile plant produces salicylic acid, the active ingredient in aspirin, and was no doubt an herbal Mexica pain reliever). The dense and durable wood of the ahuehuete was most likely used as posts for the multi-functional causeways called calzadas (more about them in a minute).
According to the noted archaeologists Pedro Armillas and William T. Sanders, the swampland converted into chinampas was estimated to be about 12,000 hectares, enough to support a population of between 117,000 – 200,000 with an annual consumption of 160 kilograms of maiz (corn) per head. What else grew on these islets? Chia, beans, squash, tomatoes, avocados, amaranth, cacao (chocolate), chilies, cotton, and a variety of flowers including marigolds, which are native to Mexico. The Mexica fished and also consumed the endemic salamander, the axolotl (Ambystoma mexicanum), named after the Aztec god of fire and lightning, Xolotl. The axolotl was important in the diet of pre-Hispanic residents of the city, along with ducks and other waterfowl that were trapped in nets.
Construction of the calzadas, the system of dikes and watery causeways, was begun in the 1420s, initially to separate the brackish from the fresh water. They most likely had openings to manage flows, similar to an agricultural sluice gate. The calzadas averaged five to seven meters wide and eight km (about 4.8 mi) in length. To form the dikes, wood posts, perhaps from the locally available black cypress or pine/oaks in the surrounding forests, were anchored in the shallow lakes and back filled with layers of rock, clay, and a mortar of mud and calcium carbonate (limestone). They required constant maintenance.
Netzahualcóyotl, the tlatoani (leader) of Texcoco – and a scholar, philosopher, warrior, architect, and poet to boot – vastly improved on this system of water management. Aside from his military victories, governmental prowess, and poetic skills, he was a superb engineer. According to Wikipedia, “He is said to have personally designed the albarrada de Nezahualcóyotl (dike of Nezahualcóyotl) to separate the fresh and brackish waters of Lake Texcoco, a system that was still in use over a century after his death.”
The construction of the calzadas took place at roughly the same time as the aggressive expansion of the Triple Alliance empire, which handily had 50,000-plus solders available from Nezahualcoyotl’s army. The calzadas also served as roadways, which ironically contributed to the conquest of the city as the Spaniards cut off supplies, particularly the aqueducts conveying water (see below for this third triumph of ancient engineering), from the mainland. The calzadas were the avenues of trade and contributed to the enormous wealth of the city, as the groups conquered by the Triple Alliance, which extended to Guatemala at its height, paid tribute to the capital.
In 1466 Nezahualcóyotl began the construction of another important hydraulic work, the Chapultepec aqueduct system. It supplied fresh spring water to Tenochtitlán. Before the aqueduct system was built, water was supplied by canoe from the springs at Chapultepec (now a large park in the middle of modern Mexico City). Water was distributed through apantles (open pipes) to public fountains and noble houses.
A second aqueduct was built by Nezahualcóyotl’s successor, Ahuítzotl, around 1500. Although Ahuítzotl had supervised a huge project to rebuild Tenochtitlán, completing the Temple Mayor (the Great Pyramid), the aqueduct project didn’t go so well. At the springs of Coyoacán, Ahuítzotal had a dam and two holding tanks built at elevations necessary to create enough pressure to send water into new aqueducts that joined the existing system. As the story goes, about 40 days after the Coyoacán aqueduct opened, it began to rain. It continued to rain. It poured. The elevated design sent high-pressure floodwaters throughout the city, Ahuítzol took refuge in the Temple Mayor, hit his head on a brand new rock, and died shortly after.
I am now out of both time and space!
For more information:
Mundy, Barbara E. The Death of Aztec Tenochtitlan, The Life of Mexico City (Austin, TX: University of Texas Press, 2015).