By tradition, the nomadic Mexica people saw an eagle perch on a cactus on a marshy islet in Lake Texcoco, took it as a sign to settle, and founded their city there around 1325. (That scene is at the centre of the Mexican flag today.) An insignificant settlement at first, within two centuries it became the capital of an empire.

The city's growth was an extraordinary feat of engineering. The Mexica built artificial farming islands called chinampas in the shallow lake — highly fertile floating gardens formed from mud and vegetation. The city was linked to the mainland by broad stone causeways; drinking water was brought in by aqueducts, and the city was divided by canals. At its centre rose the twin-shrined Great Temple (Templo Mayor).

In the 15th century Tenochtitlan became the centre of the Aztec Empire, leading a Triple Alliance with neighbouring cities that dominated a wide region. Its population may have exceeded 200,000 — larger than most contemporary European cities. This was a civilisation that developed with no contact with Europe, possessing its own writing, calendar and architecture.

In 1521 the Spanish conqueror Cortés and his indigenous allies besieged and destroyed the city; modern Mexico City was built upon its ruins. The foundations of the Templo Mayor were uncovered again in the 20th century, in the very heart of the city.