What lake was Tenochtitlan built on?

Tenochtitlan was built on an island in Lake Texcoco. The Mexica founded the city around 1325 in the Valley of Mexico, placing it on a small natural islet in the lake’s western section. As the population grew, they expanded the settlement with artificial islands, causeways, canals, and chinampa farming plots.

Lake Texcoco was a large, shallow, naturally saline lake within a closed basin. Its waters shaped the city’s engineering and daily life: causeways connected Tenochtitlan to the mainland, while dikes helped control flooding and separate fresher water from the lake’s saltier sections. The city eventually became the capital of the Aztec Empire.

A common mix-up is to say that Tenochtitlan was built on Lake Xochimilco or Lake Chalco. Those were neighboring lakes in the Valley of Mexico, but Tenochtitlan stood in Lake Texcoco. After the Spanish conquest, colonial authorities drained most of the lake to control flooding; modern Mexico City now occupies much of the former lakebed.