Because the Aztecs got the last of the land that was up for grabs in the Valley of Mexico, it wasn't rich farmland. Actually, living on an island in the middle of a swampy lake meant there wasn't much land at all. But that didn't prevent the Aztecs from growing enough food to support a population that, at its height, required 88 million pounds of corn per year to feed just the residents of the capital city, Tenochtitlan [source: Green].
So how'd they do it? The Aztecs produced prodigious amounts of corn, beans and squash, and they even raised animals such as turkeys through the use of floating gardens known as chinampas.
To create these agricultural wonders, areas of approximately 90 feet by 8 feet (27.4 meters by 2.4 meters) were staked out in the lake. These stakes were joined by poles intertwined with reeds, twigs and branches. This rectangular enclosure was then filled with mud and decaying plant matter to raise it above the surface of the lake. Willow trees (which were pruned so they wouldn't block too much sunlight) were planted around the border. As they grew, the trees helped anchor the floating plot to the lakebed.
Human manure was used as fertilizer, which served the dual purposes of providing nutrients for the crops while keeping the city clean.