How far did chinampas make Tenochtitlan possible?

The short answer

• Frost and unreliable rain threatened ordinary fields. The basin’s altitude exposed maize to two dangers. Above 2,200 metres, a September frost could arrive early, while summer rains could fail, as they did in 1452–54. Chinampa beds had moisture rising from below, and the water around them moderated the cold. Their location in the shallow lakes thus answered both problems, much as irrigation helps farmers through a dry season, although it could not prevent every crop failure.
• The dike freshened water for new fields. Fresh water was indispensable: salt kills crops. Chinampas therefore flourished in the spring-fed southern lakes. Around 1449 Nezahualcoyotl’s dike helped separate the western lagoon from salty Lake Texcoco, making more water around Tenochtitlan suitable for cultivation. By 1469 the map shows fields south of the city. A work built for flood control also helped create conditions for the later fifteenth-century expansion of farming.
• Conquest gave the state control of the best water. The freshwater farming zones belonged to communities the alliance first had to defeat. It took Xochimilco and neighboring lake towns around 1430 and the Chalco confederation by about 1465, after decades of war. The victories gave the capital access to both fields and the labor of their communities. Arco and Abrams estimate 25 million person-days over forty years for the southern fields; local communities could have supplied that work, perhaps under state direction. How far the state directed it remains debated.
• A growing city needed food on a scale no island could supply. A few thousand people lived in Tenochtitlan in the 1300s. By 1519 the number may have reached 150,000–200,000 or more on an island of about 13.5 square kilometres. Growing food intensively in the lake helped, but the city still needed supplies from elsewhere. Canoes carried nearby produce, markets gathered goods from many communities, and tribute reached beyond the basin. The search for supplies accompanied expansion toward the warm, wet Gulf coast.

What it changed

One of the world’s largest cities. The scale of the city astonished Spaniards who arrived in November 1519. Tenochtitlan and Tlatelolco together probably housed 150,000–200,000 people or more, exceeding any city in Spain. Food made such a concentration possible. Chapter 10 considers the other demands of island life: organizing water, streets, canals and waste for its inhabitants.

A food supply tied to empire. Food from distant communities helped sustain the capital, but those connections could also be broken. Provinces might rebel against tribute, and enemies could cut routes. In 1521 former subjects joined the Spaniards and blockaded the lake, turning the city’s dependence into a vulnerability during the siege described in Chapter 11.

A technique that outlived the empire. Chinampa farming survived the conquest of the empire. Fields at Xochimilco still supply vegetables and flowers in parts of southern Mexico City and form part of a UNESCO World Heritage site. Chapter 12 follows this longer history: the technique continued after the state that expanded it had fallen.