southern outskirts of Alexandria, overlooked the Potomac and the mouth of Hunting Creek.
Its site was a bluff rising about twenty-eight feet above high water.
It was armed with five 200-pounder Parrott guns and a 15-inch Rodman smooth-bore, emplaced in pairs.
The parapet was twenty-five feet thick.
The 15-inch Rodman gun visible above the bomb-proofs, can be studied below closer at hand.
This monster of its time became possible through the discoveries made by Captain Rodman, of the United States Ordnance Department.
It is mounted on a center-pintle carriage — that is, the tracks carrying the carriage are completely circular, and the pivot on which it revolves is under the center of the carriage.
The timber revetment of the interior slope of the parapet affords greater protection to the garrison; the men can stand close to the wall, and are less apt to be struck by highangle fire.
In the foreground are the entrances to the bomb-proofs, guarded by two sentries who accommodating