Question

why did the aztecs build chinampas

Answer 1

Aztec farming has become most famous because of the brilliant chinampas system that Aztec farmers used. Certainly there were a number of techniques used in the Aztec empire. But with the great city of Tenochtitlan built on swampy but rich ground, the chinampas became key to the food production of the people.

Chinampas were, of course, not just used for the capitol city, but throughout the Valley of Mexico around the lake bed. As the empire grew, more sources of food were required. At times this meant conquering more land, other times it meant expanding the chinampa system.