They built a capital in the middle of a lake.

The Mexica, as the Aztecs called themselves, told of a migration from a homeland called Aztlan, whose location is unknown; many scholars place their arrival in central Mexico in the 13th century.1 Their god Huitzilopochtli, the story goes, told them to settle where they saw an eagle eating a snake on a cactus. Archaeologists date the founding of Tenochtitlan to 1325 CE.1

Tenochtitlan began as a small city-state paying tribute to its neighbors. In 1428 it joined Texcoco and Tlacopan in the Triple Alliance, which came to control the region.1

The city sat on an island off the western shore of Lake Texcoco, enlarged by hand to more than five square miles. Scholars estimate 200,000 to 250,000 people lived there in 1500, more than four times the population of London at the time.2

Six major canals and many smaller ones made boats the main way to get around. Three causeways with drawbridges linked the island to the shore, and an aqueduct brought fresh water from a spring at Chapultepec.2 Farmers grew corn, beans and squash on chinampas, raised fields built up out of the shallow lake.2

As many as 25,000 people came to the city's market each day. Judges settled disputes, and cacao beans, copper axes and woven capes served as standard units of value.2

Records of tribute and religious life were kept in painted books. Two that survived the conquest, the Codex Mendoza and the Matrícula de Tributos, list the goods each town owed.1

Spanish forces under Hernán Cortés arrived in 1519. After a siege that began in May 1521, the city surrendered on August 13, 1521, and much of it was destroyed. Mexico City was built on its ruins.1

The Mexica's language, Nahuatl, lives on: Mexico's 2020 census counted about 1.65 million speakers.3

A tribute list in the Codex Mendoza is a record you read at a glance: pictures of goods, repeated to show how many.1 A QR code is the same idea for a phone. The picture is the data.