Florida's Fort under Six Flags
"I will take St. Augustine or leave my bones before its walls," claimed British General James Oglethorpe in 1740. He did neither. While he did raze part of the Florida city, he could not crack the Castillo de San Marcos and retreated from Spain's impenetrable fortress after a 38-day siege. The Castillo never fell to an enemy attack—only to international treaties.
Today the Spanish fort—a national monument supervised by the National Park Service—is a museum of American military history. Begun in 1672, the fort protected St. Augustine and controlled the shipping routes between the New World and Europe. Its walls were the heart of its defenses. Built of coquina (seashells crushed together over millions of years), they were impervious to cannon fire. Heavy balls either bounced off the walls or embedded themselves without cracking the defenses.