Baths of Diocletian (306 CE)
Roman Emperor Diocletian built his baths to impress, and that impression has shockingly lasted almost two thousand years. His Baths are the largest known from the Roman Empire, outsizing even the luxurious Baths of Caracalla. The bathing complex, with its traditional caldarium (hot baths), tepidarium (warm baths) and frigidarium (cool baths), recreational areas, an additional outdoor pool and gardens, served up to 10,000 people every day (3,000 at a time) for about 250 years.
In the 160th century, as the Roman Catholic Church came to power, Pope Pius IV commissioned Michelangelo to restructure the frigidarium and tepidarium into a Basilica. Michelangelo retained as much of the original baths as he could, including the Egyptian red marble columns and their Corinthian capitals. But there were some necessary changes; since the ground level outside had risen, Michelangelo raised the Basilica floor 2 meters (6 feet) to match the terrain.
