Fort Don Carlos de Barrancas--the word Barrancas signifying _broken ground_--was so named on account of the rugged appearance of the site on which the fort stands. The first fortification is supposed to have been built by a commander named Auriola, in 1687, as a defense against the French. It was a square, with bastions, situated near the site of the present Fort Barrancas. What remains of the ancient fort was built by the Spaniards--it being a tetragon, with salient angles at each corner, and formerly had a tower one story higher than the curtains, which served as a point for reconnoisance. It has an outer scarp, or glacis, surrounded by a barbette twenty-two feet wide. It contains an embrasure, the firing being done from the loop-holes and parapets with flank defenses. The barbette is overgrown with weeds and cactus, all armed with projectiles more to be dreaded than any other weapons of warfare in position here now. A deep dry-well is visible near one corner of this barbette, supposed to contain the buried treasure of the Spanish Governor, and for which it is said he ordered three of his men to be killed to prevent their divulging the secret. No guns are mounted on the parapet but two Rodmans of one hundred pounds caliber. The entrance to the old fort is through a scarp gallery several hundred feet in length. At the terminus are three arched rooms, the arches constructed without nails, from native pine boards, the grooves being fitted to each other. Here was the Governor's chamber for council, the ordnance department, and barracks. The materials employed for the walls were only brick and mortar, both in the old part built by the Spaniards, and the new constructed by the Americans. From the form and thickness of one part of the fort, it is supposed to contain a dungeon, but no efforts have yet been made at excavation, to explore its hidden secrets. The entire fortress, both ancient and modern, is surrounded by a dry moat, the main entrance having a portcullis. The present fortification of Fort Pickens was built in 1830. It is situated on a strip of land fifty miles in length, and only one-half mile in width, called Santa Rosa Island. This ground has been the scene of various conflicts during its early settlement, of which we have a record for nearly two centuries. The contests between the Spanish and French were always severe, the victor destroying the forts and devastating every thing within reach--which accounts for the disappearance of the ancient landmarks. Fort St. Michael and Fort St. Bernard were other works of defense built in the rear of Pensacola, but designed originally to protect the town and harbor, and also to serve as a safeguard against the Indians. The principal fort, St. Michael, was attacked in 1781 by Don Galvez, when a bomb-shell struck the eastern glacis of Fort St. Bernard, and, in rebounding, blew up the magazine, destroying the principal redoubt, which compelled the garrison to surrender by capitulation.