Tenochtitlan (Nahuatl languages: Tenōchtitlan pronounced [tenoːt͡ʃˈtit͡ɬan]; Spanish: Tenochtitlán), also known as Mexica-Tenochtitlan (Nahuatl languages: Mēxihco Tenōchtitlan pronounced [meːˈʃiʔko tenoːt͡ʃˈtit͡ɬan]; Spanish: México-Tenochtitlán), was a large Mexica city-state in what is now the center of Mexico City. The exact date of the founding of the city is unclear. The date 13 March 1325, was chosen in 1925 to celebrate the 600th anniversary of the city. The city was built on an island in what was then Lake Texcoco in the Valley of Mexico. The city was the capital of the expanding Aztec Empire in the 15th century until it was 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 in the historic center of the Mexican capital. The World Heritage Site of Xochimilco contains what remains of the geography (water, boats, floating gardens) of the Mexica capital. Tenochtitlan was one of two Mexica āltēpetl (city-states or polities) on the island, the other being Tlatelolco.