The Aztecs were originally made up of nomadic hunters. They wandered for centuries until they reached northern Mexico. Here they searched for fertile land that had the potential to be farmed. In 1325 the Aztecs settled on a marshy island near the western tip of Lake Texacoco. They began to build a new city, which was the largest in the world before the Spanish conquest. Tenochtitlan was founded in this small island on Lake Texacoco. Gradually this island was extended further into the lake. This was done by building artificial islands or " floating gardens". These were very fertile and the city prospered. Marshy areas were filled with soil from the lakeshore, and towns were built around Tenochtitlan.
An island had many advantages for the Aztec empire. One was defense, because invading enemies could not march over water. They could only approach from three bridges connecting the island to the mainland. In times of war the Aztec soldiers would wait for the enemy to climb aboard the bridges and then cut the ropes. Then they would bombard them with a hail of arrows and spears while they were in the water. Another advantage of living on an island was transportation. It was easier to carry goods by canoe than to use people. The Aztecs didn't use animals or wheels for transportation.
Since the land was so fertile, an abundant amount of food could be farmed. The main crops were corn, beans, squash, amaranth, and chili.
Precious stones and gold could be found on the shores of Lake Texacoco.
As you can see, what was a leftover piece of swampland, later emerged into the birthplace of a fierce and powerful people who ruled over Mexico, The Aztec.