, also known as Mexico-Tenochtitlan,{{efn| ; {{lang-es|México-Tenochtitlan'}}}} was a large Mexican in what is now the historic 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 are in the historic center of the Mexican capital. The World Heritage Site of contains what remains of the geography (water, boats, floating gardens) of the Mexica capital. was one of two Mexica (city-states or polities) on the island, the other being . The city is located in modern-day Mexico City. Etymology Traditionally, the name was thought to come from Nahuatl ("rock") and ("prickly pear") and is often thought to mean, "Among the prickly pears [growing among] rocks." However, one attestation in the late 16th-century manuscript known as "the Bancroft dialogues" suggest the second vowel was short, so that the true etymology remains uncertain. Another view is that the city was named after Tenoch. Geography covered an estimated , situated on the western side of the shallow Lake Texcoco. At the time of Spanish conquests, Mexico City comprised both and . The city extended from north to south, from the north border of to the swamps, which by that time were gradually disappearing to the west; the city ended more or less at the present location of . The city was connected to the mainland by bridges and causeways leading to the north, south, and west. The causeways were interrupted by bridges that allowed canoes and other water traffic to pass freely. The bridges could be pulled away, if necessary, to protect the city. The city was interlaced with a series of canals, so that all sections of the city could be visited either on foot or via canoe. Lake was the largest of five interconnected lakes. Since it formed in an endorheic basin, Lake was brackish. During the reign of Moctezuma I, the "levee of " was constructed, reputedly designed by .