When the Aztec arrived in the area that is now Mexico, they found the land was mostly occupied by other peoples. The only land they could use was around the swampy edges of a lake.

So they set about reclaiming the edges of the lake by making raised beds, something like huge baskets filled with lake mud. The beds rose above the surface of the lake. The mud was very fertile, so crops grew in it easily. This allowed many Aztec to live in a small area and prosper.

The mud dug out of the lake made canals in which fish swam and so could be caught and eaten for food.