This is one of three buildings that made up the main plantation house. The others were first burned at the end of the US Civil War, and then ruined in the big earthquake of 1886.
The brick wall below was built up from the bricks that remained after the earthquake.

A little trivia fact; Most people think of southern plantations as having big white buildings, huge porches, and tall columns. We have them, however most structures built after the late 1700’s were made of brick. Marshes have plenty of mud and they make great bricks.
Most important, bricks don’t burn. manor homes, churches, and cities burned often until bricks were used.