Spain commissioned El Morro in 1539 because Puerto Rico was the stepping-stone — the passage from Europe to Cuba, Mexico, and the American continents. Everything that followed proves the calculation right. Sir Francis Drake attacked by sea and lost. A subsequent English force came overland, found the one crack in El Morro's armor, took the city — then dysentery drove them out before they could hold it. The Dutch couldn't force a surrender and burned San Juan on their way out. Meanwhile, up the hill on what the Spanish renamed from Gallows Hill, Castillo San Cristóbal took 150 years to complete and covered 27 acres — the largest fortification ever built in the New World. In 1797, its defenses repelled a British invasion force of seven thousand. In 1898, its guns fired the first shot of Puerto Rico's entry into the Spanish-American War. The walls between 18 and 25 feet thick still stand at 140 feet above the Atlantic. The stakes that built them are still legible in the stone.
