The Charleston Post Office is one of the oldest in the United States , having been established by George III in 1740 , during the provisional colonial governorship of William Bull . The site of today 's U.S. Post Office and Courthouse was originally called Trott 's wharf . A guardhouse and armory was built there in the 1830s . Colonel Isaac Hayne was incarcerated in the basement and executed by the British in this complex in 1781 . The guardhouse was destroyed during the devastating 1886 Charleston earthquake . A decade later , the site was redeveloped
1886 Charleston earthquake
1886 Charleston earthquake
United States Post Office and Courthouse (Charleston, South Carolina)