The Aztecs were located in central Mexico, primarily in the Valley of Mexico where Mexico City now stands. They founded their capital city, Tenochtitlán, in 1325 on a small island in Lake Texcoco. This area was a fertile and heavily settled central zone surrounded by lakes and mountains. The Aztec Empire eventually extended over a large region of central and southern Mexico, ruling an empire composed of many city-states covering around 80,000 square miles with millions of inhabitants.