At its northern end is Fort Marion and at the southern end St. Francis Barracks, the United States military post, so named because it occupies the site of the old Convent of St. Francis, having some of its coquina walls incorporated in the present structure. The harbor in front, which in past centuries sheltered so many Spanish fleets and those of Spanish enemies as well, is now chiefly devoted to yachting. When Menendez and his Spaniards first landed they built a wooden fort commanding the harbor entrance, surrounded by pine trees, which they named San Juan de Pinos. This was afterwards replaced by Fort San Marco, constructed of coquina, which was nearly a hundred years building, and was finished in 1756. Upon the transfer of Florida to the United States this became Fort Marion. It is a well-preserved specimen of the military architecture of the eighteenth century, built on Vauban's system, covering about four acres, with bastions at the corners, each protected by a watch-tower, and is surrounded by a moat, the walls being twenty-one feet high. The fort is in reasonably good preservation, and is said to have been constructed mainly by the labor of Indians. It took so long to build and cost so much under the wasteful Spanish system that one sovereign wrote that it had almost cost its weight in gold; yet it was regarded then as supremely important to be finished, being the key to the Spanish possession of Florida. Over the sally-port at the drawbridge are carved the Spanish arms and an inscription recording the completion of the fort in 1756, when Ferdinand VI. was King of Spain and Don Hereda Governor of Florida. It mounted one hundred of the small guns of those days, and the interior is a square parade ground, surrounded by large casemates. Upon each side of the casemate opposite the sally-port is a niche for holy water, and at the farther end the Chapel. Dungeons and subterranean passages abound, of which ghostly tales are told. This fort is the most interesting relic of the ancient city, a picturesque place, with charms even in its dilapidation.