The Aztec Empire was located in central Mexico, primarily in the Valley of Mexico where modern Mexico City now stands. The empire's capital was Tenochtitlan, an ancient city founded around 1325 on small islands in Lake Texcoco. The Aztec Empire spread over a large area in central and southern Mexico, covering up to 80,000 square miles at its height, with the capital being a densely populated and well-planned city connected to the mainland by causeways.