Which city was the capital of the Aztec empire?

Tenochtitlan, built on an island in Lake Texcoco and holding perhaps 200,000 people - larger than any European city of its day, with aqueducts, causeways with removable bridges, a vast market, and floating gardens called chinampas that produced several harvests a year.

The chinampas are the engineering that made it possible. Rectangles of lake bed staked out, layered with mud and vegetation, anchored by willows, and separated by canals - enormously productive, self-irrigating, and still worked today in the remnants at Xochimilco. A city that size on an island required feeding, and this is how it was done.

The Spanish destroyed it and built on top, and Mexico City has been sinking into the drained lake ever since - in places by more than ten metres over the last century, as groundwater extraction compacts the clay. The Templo Mayor was found by accident in 1978 by electricity workers laying cable, a few metres from the cathedral, and its excavation required demolishing colonial buildings above it - which is about as literal a rendering of a country's layered history as archaeology offers.