PYRAMIDS IN A NATIONAL CEMETERY
These pyramids (made of the rock shell substance coquina) are in the small U.S. National Cemetery in St. Augustine, Florida. The plaque says that 1,466 soldiers killed in the Indian Wars are buried beneath them.
The cemetery grew around the pyramids. I could find nothing to explain the significance in choosing these symbols (at that particular time and place) for fallen soldiers of war.
Interesting esoteric thought was used in the early 1800s in northern Florida, in a territory originally settled by the Spanish, and a fairly new U.S. territory.
The Indian Wars in which these soldiers died were from 1835-1843.