According to their mythology, the Aztecs built Tenochtitlan on an island surrounded by swamps because they were led to the location by their primary god, Huitzilopotchtli. Modern historians believe that the Aztecs settled on the island and built their city there in 1325 because they were the late arrivals in a wave of migration that began after the fall of the earlier Toltec civilization. As one of the last groups to arrive in the region, the island in the middle of a saline marsh was the only piece of dry land left available to them.
Another explanation offered by historians for the decision to build a city in an area surrounded by marshland is that the Aztecs saw the value of an urban center that could make ample use of a naturally available waterborne communication and transportation network. The marshes also provided nearby fish and fowl food resources and were a convenient source of medicinal and edible aquatic plants.