On this day in history, July 24, 1911... While searching for the lost city of Vilcabamba, Yale professor Hiram Bingham rediscovered the famous Machu Picchu estate, which is believed to have been built by the Incas around 1450, high atop a hill in the Andes Mountains, in Peru. The citadel was abandoned a century later during the Spanish Conquest. There is evidence to suggest other explorers had knowledge of the city before Bingham, but Bingham is credited with its rediscovery and for bringing it to international attention. It is now widely believed that Machu Picchu was built as a royal estate for Pachacutec Inca Yupanqui. The site remains mysterious because it has no defensive wall, which is uncharacteristic of a fortress. It has fountains, temples, and strange altars. It is believed that the people who built it did not have iron tools or the wheel, so it is unknown how they managed to cut the stone so perfectly so as to not even need mortar.