Mexico City was built on the ruins of Tenochtitlan, the capital of the Aztec Empire. The city of Tenochtitlan was built in 1325 on an island off the western shore of Lake Texcoco in the Valley of Mexico (Valley Anahuac).

According to Aztec mythology, Huitzilopochtli, the god of war, sent them to go to a new place beyond their former lands and build a city on the spot where they saw an eagle sitting on a cactus and devouring a snake.

The Aztecs built an extensive network of canals and artificial islands – chinampas. These so-called “floating islands” were also used for agricultural purposes, providing high yields and feeding a growing population.

Over time, Mexico City grew and expanded, the canal systems were filled to build roads, and the foundation of the lake bed was forgotten. This led to the overuse of groundwater, soil collapse, and flooding of the city.

Canals of Xochimilco

The canals of Xochimilco are not only a popular destination for boat trips. These canals and the man-made islands that surround them – chinampas – are silent witnesses to Mexico City’s distant pre-Columbian past.

The technology for making chinampas was developed in Mesoamerica before the Aztecs, but it was the Aztecs who used it on a huge scale. Despite the common term “floating gardens”, chinampas do not actually float.

Famous chinampas are built by creating a fence using wooden stakes on the lake. This enclosure is then filled with alternating layers of mud and decaying vegetation until solid ground is formed above the water level.

An artificial island is thus formed and trees are planted along the edges since the roots of the trees help prevent erosion.

Chinampas of Xochimilco

Chinampas are artificial islands held together by wooden stakes and tree roots. The mixture of dirt and vegetation makes the soil very fertile and is one of the reasons why the chinampas are extremely productive.

The canal water also contains fish, which not only provides more food but also adds nitrogen-rich manure, which in turn fertilizes the plants. The fish in the canals from which chinampa was prepared had benefits.

Fish served as an additional source of food, and played a crucial role in fertilizing crops. Their nitrogen-rich excrement acted as a natural fertilizer for plants grown, increasing the agricultural productivity of chinampas.

This farming system was an ingenious way to maximize agricultural efficiency.

Generally, no irrigation is required as the plants absorb water directly from the channels, and overuse of water is prevented as the plants only absorb the water they need. The system is also drought and flood-resistant.

Chinampas that are used today function a little differently. Greenhouses are usually used. Today, instead of producing food, Xochimilco’s chinampas are mainly used to grow the flowers for which Xochimilco is famous.

The also Aztecs grew flowers in the chinampas of Xochimilco. Xichimilco means “garden of flowers” in the Nahuatl language. However, since chinampas are very productive, they are also good for small-scale farming.

Chinampas are very productive, and although today they are mainly used for growing flowers, they also have the potential for efficient food production, which could help reduce poverty and improve food security.

The network of canals and chinampas in Xochimilco today is just a glimpse of what it used to be. Urban sprawl, climate change, pesticides, pollution, and neglect are all contributing to the slow destruction of the chinampas.

Today, these systems of canals and chinampas face many threats, and one of them is the spread of invasive water hyacinths, which can be seen congregating near the shorelines, posing challenges to the local ecosystem.

From a floating city to a sinking city

The Aztecs were great engineers. The canals and chinampas of Xochimilco are only a small part of the original network of canals and artificial islands that spanned the city of Tenochtitlan and its surrounding areas.

These canal systems were connected to a system of dams, levees, and aqueducts that together helped provide water to the inhabitants of Tenochtitlan while simultaneously controlling the water levels in the canals.

The Aztecs also used terraces and irrigation canals to produce enough food.

When the Spanish arrived, Tenochtitlan had about 200,000 inhabitants. But the Aztecs could not even dream that several centuries later a metropolis with a 20 million population would lie on the same foundation.

The Spaniards drained canals, and the land began to appear solid, but the former lake bed could never be truly solid. When the system of aqueducts and canals collapsed, Mexico City began to pump out groundwater.

And then the problems began…

Groundwater is being drawn from aquifers beneath Mexico City faster than it is naturally replenished, causing the land to subsidence. This process causes buildings to lean and crack as the ground beneath them settles.

Many buildings in Mexico City are leaning because the ground beneath them is eroding due to overuse of groundwater. In this context, the canals and chinampas of Xochimilco serve as silent reminders of the city’s past.

Chinampas were commonly used in pre-Hispanic Mexico and Central America. The Aztec farmers used to build chinampas for agricultural purposes on freshwater lakes in the Valley of Mexico, including Lake Texcoco.

The word “chinampa” comes from the Nahuatl word “chināmitl” (“square made of canes”) and the Nahuatl locative, “pan”. Spaniards used the word “camellones” (“ridges between the rows”) to describe chinampa gardens.

Chinampas were also called floating islands because of the illusion they created.

What are chinampas?

Chinampas are man-made agricultural plots constructed on shallow lakes. Far from being true “floating gardens”, these plots were anchored to the lakebed using wooden stakes and surrounded by a network of canals.

By layering lake mud, sediment, and decaying vegetation, the Aztecs created rich, fertile soil that supported intensive crop production. Thus, chinampas turned the shallow lakebed into highly productive “floating” farmland.

Origins and historical context

The first chinampas were built around 1100 in Culhuacan. The chinampa system spread and became more widely used in the Valley of Mexico between 1150 and 1350, particularly around Lakes Xochimilco and Chalco.

The Aztecs did not invent chinampas, but they were the first to develop them for large-scale cultivation. They used fertile soil from lake beds to create chinampas, which allowed them to grow crops such as corn, and beans.

The chinampa system emerged out of necessity in the Valley of Mexico, where fertile land was scarce due to the region’s geography. The growing Aztec Empire needed a reliable food source to sustain their growing population.

By the height of the Aztec Empire in the 15th century, chinampas were central to feeding the increasing population of Tenochtitlan, the Aztec capital, which was estimated to be 200,000 people, according to historical records.

Each chinampa garden could yield up to seven harvests per year. This intense agricultural output was an important key to the Aztecs’ ability to sustain their increasing urban population and support their expanding empire.

Key crops grown included:

• Maize (corn): A staple of the Mesoamerican diet.
• Beans: A crucial protein source.
• Squash: A versatile crop used in numerous dishes.
• Chili peppers: Essential for flavoring food.
• Amaranth: A nutrient-dense grain.

How were chinampas constructed?

The construction of chinampas required meticulous planning and considerable labor. It was a multi-step process that transformed the shallow lakes of the Valley of Mexico into fertile, productive farmland.

The process began by staking the boundaries: wooden stakes were driven into the lakebed to outline the rectangular shape of the chinampa. These stakes served as the foundation and marked the perimeter of each plot.

Next, the Aztecs wove a base by interlacing reeds and branches between the stakes. This structure provided a stable framework for the chinampa and prevented the soil from washing away.

The layering of fertile material followed, with mud, lake sediment, and decaying vegetation piled onto the base to create nutrient-rich soil. This fertile mix not only provided a robust foundation for crops but also helped retain moisture, crucial for the plants to thrive.

To reinforce the edges, willow trees were planted along the borders of the chinampa. The extensive root systems of the willows acted as natural anchors, stabilizing the chinampa and preventing erosion.

This careful attention to edge reinforcement was essential for ensuring the long-term sustainability of the structure.

The Aztecs also took care to irrigate the chinampas, digging canals around the plots to ensure a constant supply of water. These canals facilitated the transportation of goods and allowed farmers to regulate the water levels of their gardens.

Finally, ongoing maintenance was necessary to keep the chinampas in good condition.

The Aztecs regularly replenished the soil with new layers of organic material and kept the irrigation channels clear, ensuring the chinampas remained highly productive throughout the growing seasons.

The Aztecs also developed a drainage system. They dug canals to allow water and sediment to pass through. These canals collected dirt, which was then dug up and placed on top of the chinampas, helping to keep the area clean.

Agricultural productivity of chinampas

The fertility of chinampas was unmatched.

The nutrient-rich soil and constant availability of water allowed farmers to grow crops year-round. In addition to high yields, chinampas were highly diverse ecosystems, supporting not only crops but also aquatic plants and fish.

Farmers employed crop rotation and intercropping techniques to maintain soil health and maximize output. For example, maize, beans, and squash were often planted together, which enhanced soil fertility and minimized pests.

Environmental benefits of chinampas

Chinampas were not only a triumph of human ingenuity but also an example of ecological sustainability.

• Chinampa helped regulate water levels, reducing the risk of flooding.
• Canals provided habitats for diverse species, creating a balanced ecosystem.
• The organic material sequestered carbon, reducing greenhouse gases.
• Willow trees and dense vegetation prevented soil from washing away.

Cultural and economic impact

Chinampas were integral to the Aztec way of life. The productivity of chinampas freed up labor for other pursuits, such as arts, warfare, and governance, allowing the Aztecs to build a highly stratified and complex society.

The surplus produce from chinampas fed markets across the empire. For Aztecs, chinampas were a symbol of their connection to the earth and water. Ceremonies and rituals were often performed to honor this relationship.

Chinampas in Tenochtitlan

Tenochtitlan faced problems due to constant expansion and limited space. Chinampas were a source of fresh food in Tenochtitlan. The chinampas grew corn, beans, pumpkins, amaranth, tomatoes, chili peppers, and flowers.

To sustain the growing empire, conquering new lands or expanding the chinampa system became necessary. Chinampas played a crucial role in supplying food, evident in tribute records showing farmers’ relatively light tribute compared to others.

In Tenochtitlan, the chinampas ranged from 90×5 m to 90×10 m. Chinampas were separated by channels wide enough for a canoe to pass. These raised, well-watered beds had very high crop yields with up to 7 harvests a year.

Chinampas were created by staking out the shallow lake bed and then fencing in the rectangle with wattle. The fenced-off area was then layered with mud, lake sediment, and decaying vegetation, eventually bringing it above the level of the lake.

Often trees were planted at the corners to secure the chinampa. In some places, the long raised beds had ditches in between them, giving plants continuous access to water and making crops grown there independent of rainfall.

Decline and challenges

After the Spanish conquest of the Aztec Empire and the fall of Tenochtitlan, the chinampa system began to decline. The colonizers drained Lake Texcoco to control flooding and expand Mexico City, destroying vast areas of chinampas.

Today, the remnants of the chinampa system survive in Xochimilco, which is considered a model of modern sustainable agriculture. While many farmers are happy to return to their agricultural roots, they face several challenges.

However, they face numerous threats, including:

• Expansion of Mexico City has encroached on chinampa areas.
• Industrial and agricultural runoff has degraded the water quality.
• Non-native plants and animals disrupt the ecosystem.

Other problems include limited water supply, the widespread use of pesticides, the impact of climate change, urban sprawl, and water pollution problems associated with untreated sewage and toxic waste.

Chinampas in our days

There is a growing recognition of the value of chinampas as a model for sustainable agriculture. Efforts are underway to restore and preserve the system in Xochimilco, both for its cultural heritage and its potential applications in urban farming.

Chinampas offer a blueprint for addressing food security in cities.

Their space-efficient design, high productivity, and ecological benefits make them ideal for modern urban environments. Research is ongoing into how chinampa-inspired techniques can be adapted for contemporary use.