Battery Buchanan is situated at the very southern end of what is called Federal Point, the culmination of the peninsula formed by the Cape Fear River and the Atlantic Ocean south of Wilmington. At one time the favored Civil War blockade-running to Wilmington was here at what was called New Inlet.
However, after the war, it was decided that New Inlet was silting the main channel of the Cape Fear River and in the 1870s, a dam, referred to now as "The Rocks" was built across it, damming up the inlet. It still stands, but there is talk of tearing it down (see my posts in my Naval History Blog, Running the Blockade).
It was engineered by the father of the man who built the Lincoln Memorial in Washington, D.C., who used some of his father's technique in the construction of the memorial since it was built on previously swampy land.
I've walked parts of "The Rocks" many times, but never all the way across it.