The Aztecs found Tenochtitlan

According to tradition, the Mexica founded Tenochtitlan on an island in Lake Texcoco in 1325. It grew into the capital of the Aztec Empire.

The date comes from tradition and is approximate.

Context

Britannica dates the founding to about 1325 and describes the city as beginning on two small islands in Lake Texcoco in the Valley of Mexico. The Mexica were a late-arriving group who settled on land no one else wanted, and tradition says a god guided them to the site.

The island city grew through artificial plots and was linked to the shore by several causeways. It eventually covered more than 5 square miles (13 square kilometers) and became the heart of the Aztec Triple Alliance with the cities of Texcoco and Tlacopan.

The Spanish under Hernan Cortes captured it on 13 August 1521 after a siege. Mexico City was built on its ruins, and the founding year is a traditional date rather than a precisely documented one.

The city was divided into four districts and had a great temple precinct at its center, the Templo Mayor, where major rituals took place. Accounts from Spanish soldiers who saw it in 1519 described a city larger and busier than most in Europe. Archaeologists uncovered the Templo Mayor in the 1970s beneath modern Mexico City. Dates before the 15th century come from later Indigenous and Spanish writings and should be read with caution.