How did the Aztecs build Tenochtitlán?
The Aztecs built Tenochtitlán on an island in Lake Texcoco by driving wooden stakes into the lake bed, filling them with rocks and soil, and creating chinampas (floating gardens) for agriculture. They connected the island to the mainland via causeways, built aqueducts for fresh water, and constructed massive pyramid-temples — creating a city of 200,000+ people.
Tenochtitlán, the capital of the Aztec Empire, was one of the most remarkable feats of urban engineering in the pre-modern world. Built on a small island in Lake Texcoco in the Valley of Mexico, it grew from a humble settlement founded in 1325 to a metropolis of 200,000–300,000 people by the early 16th century — larger than any city in contemporary Europe.
The Aztecs expanded their island through a technique called chinampa agriculture. Workers drove wooden stakes into the shallow lake bed, creating rectangular enclosures that were filled with layers of vegetation, mud, and soil. These artificial islands — the famous 'floating gardens' — were extraordinarily productive, allowing multiple harvests per year and supporting a dense urban population. The canals between chinampas served as transportation routes, creating a Venice-like city navigable by canoe.
Three major causeways, each wide enough for eight horsemen abreast (according to Spanish accounts), connected the island to the mainland. These causeways incorporated removable bridges that could be raised for defense. Two aqueduct systems — one from Chapultepec, another from Coyoacán — brought fresh water to the city, since Lake Texcoco's water was brackish.
At the city's heart stood the Templo Mayor, a massive dual pyramid-temple dedicated to the rain god Tlaloc and the war god Huitzilopochtli. The central precinct also included palaces, a great marketplace (Tlatelolco, where 60,000 people reportedly traded daily), ball courts, and administrative buildings. The Spanish conquistadors, who had seen the great cities of Europe, were astonished. Bernal Díaz del Castillo wrote that the sight was 'like the enchantments they tell of in the legend of Amadís... some of our soldiers even asked whether the things that we saw were not a dream.'