Built by the British in 1771 as an Exchange and Customs House, this Palladian-style building was where South Carolina Patriots ratified the US Constitution in 1788. Some of the very men who signed the document had been imprisoned downstairs in the gloomy Provost Dungeon (visit by guided tour only) during the British occupation of the city. Visitors to the dungeon today can see part of the original wall built in 1690 to fortify the city.