The Mexica founded Tenochtitlan in 1325 as an "altepetl" (city-state) located on an island in Lake Texcoco, in the Valley of Mexico. It became the capital of the expanding Aztec Empire in the 15th century, until captured by the Spanish in 1521. At its peak, it was the largest city in the Pre-Columbian Americas. It subsequently became a "cabecera" of the Viceroyalty of New Spain. Today the ruins of Tenochtitlan are located in the central part of Mexico City.