Artillery Redan
The palisade was interrupted at this point for an artillery redan, an earth structure designed to protect two canons. The lower sections in the wall of the redan indicate where the muscle of each gun would protrude. Of the three dozen or so redans that once existed along the River Line, this is the only one that remains.
By far the most common cannon used by both sides was a 12-pounder Napoleon, a smoothbore gun. The Napoleon didn't have the range or accuracy of the rifled gun, but it could fire many different types of ordnance (shot, shell, grape, canister, etc.) and could be used to duel the opposing artillery, shell enemy troops at a distance, or blast attacking infantry.
This photo, taken by George N, Barnard, shows a Napoleon in the defense of Atlanta while federal troops occupied the city in September 1864. This same cannon is on display in the Kennesaw Mountain National Park Visitor Center, about ten miles northwest. While we don't know for certain which artillery unit occupied this redan, we do know that all the batteries that were assigned to this section of the River Line were equipped with 12-pounder Napoleons or 3-inch ordnance rifles.
Plaque courtesy Lat34North.com.
Original page, with additional info, here.
Photo credit: Byron Hooks of Lat34North.com.