How far did chinampas make Tenochtitlan possible?

The short answer

• Frost and unreliable rain threatened ordinary fields. At over 2,200 metres, rain-fed maize risked early frost in September and depended on summer rains that could fail, as they did in 1452–54. Chinampas avoided both dangers, since water seeped up from below and the lake moderated the night-time cold. The technique was therefore an adaptation to the basin’s particular climate, turning the lake’s shallow margins into the safest farmland available, much as irrigation protects modern farmers against a dry season.
• The dike freshened water for new fields. Chinampas need fresh water, because salt kills crops, so they flourished in the spring-fed southern lakes and could spread around Tenochtitlan only after Nezahualcoyotl’s dike separated the western lagoon from salty Lake Texcoco around 1449. On the map, chinampa fields appear in the lagoon south of the city by 1469. Hydraulic engineering and farming innovation reinforced each other, since each made the other more valuable. The chinampa boom of the later fifteenth century was therefore a by-product of flood control.
• Conquest gave the state control of the best water. Control of the freshwater lake towns tied farming to conquest. The alliance conquered Xochimilco and the lake towns around 1430 and the Chalco confederation by about 1465, after decades of war. Control of these towns gave the Mexica state access to the largest freshwater farming zones in the basin and the labour of the people who worked them, so that agricultural expansion followed military victory. Imperial power and chinampa farming grew together, each paying for the expansion of the other.
• A growing city needed food on a scale no island could supply. Tenochtitlan’s population grew from a few thousand in the 1300s to perhaps 150,000–200,000 or more by 1519, crowded onto about 13.5 square kilometres of island. Even the most intensive farming in the lake could not feed such numbers, so the city drew on markets and tribute from far beyond the basin. Growth itself drove the search for new sources of food, which pulled the empire outward toward the warm, wet lowlands of the Gulf coast.

What it changed

One of the world’s largest cities. The food system made possible one of the largest cities on earth, since by 1519 Tenochtitlan and Tlatelolco together probably held 150,000–200,000 people or more, larger than any city in Spain at the time. The scale astonished the Spaniards who arrived in November 1519, and Chapter 10 shows how its planners organised such numbers on an island, with water, streets, canals and waste all managed together as a single system.

A food supply tied to empire. Because the city depended on tribute and trade from distant provinces, any disruption of the empire threatened its food. Provinces that resented tribute could rebel, and enemies could cut supply routes. In 1521 the alliance’s former subjects joined the Spaniards and blockaded the lake, so the dependence that had fed the city became a weapon against it, as Chapter 11 explains.

A technique that outlived the empire. The chinampas of Xochimilco survived the conquest and are still farmed in parts of southern Mexico City today, where they form part of a UNESCO World Heritage site and supply vegetables and flowers. The longevity of the technique contrasts with the fall of the empire that expanded it, a pattern the epilogue explores, in which a farming technique outlasts the state that once commanded it.