Tenochtitlan was a Nahua altepetl (city-state) located on an island in Lake Texcoco, in the Valley of Mexico, says Wikipedia.
Founded in 1325, it became the seat of the growing Aztec empire in the 15th Century, until captured by the Spanish in 1521.
It subsequently became a cabecera of the Viceroyalty of New Spain, and today the ruins of Tenochtitlan are located in the central part of Mexico City.
“ When we saw so many cities and villages built in the water and other great towns on dry land we were amazed and said that it was like the enchantments (...) on account of the great towers and cues and buildings rising from the water, and all built of masonry. And some of our soldiers even asked whether the things that we saw were not a dream? (...) I do not know how to describe it, seeing things as we did that had never been heard of or seen before, not even dreamed about. ”
—Bernal Díaz del Castillo, The Conquest of New Spain[2]