This is Soldiers Ground, a military cemetery.
I found a plaque in the grass that I have passed any number of times. It described this section of land, in old Magnolia Cemetery.

The land was appropriated by the Confederate State Of America as a burial ground for military personnel lost in battle. I had assumed it was something like that.

Magnolia Cemetery is the resting place for many old Charleston families and as such there are military grave sites all through out the old sections. Not just Civil War, but all wars. Given the age of the cemetery and location the number of CSA graves is not surprising.
Solidiers Ground is not just South Carolina natives. A walk through the stones shows military members from all over the CSA.
A stroll through old Magnolia is a history lesson.