Built by Spanish colonialists, Mexico City was actually constructed right on the ruins of the ancient Aztec city of Tenochtitlan. The whole city, including the Great Pyramid of Tenochtitlan, was destroyed by the Spanish conquistador Hernan Cortes during his conquest of the Aztec empire. As a result, beneath the modern city lies a rich treasure trove of archaeological remains.
Various excavations have subsequently been conducted under the modern city, and an especially exciting find was announced in June 2017. The discovery was located in a side alley near the Metropolitan Cathedral of the Assumption of the Most Blessed Virgin Mary into Heaven, which was built by the Spanish and dates back to the 16th century.