Castillo San Felipe del Morro

Castillo San Felipe del Morro, commonly called El Morro, guards the entrance to San Juan Bay on the northwestern point of the islet of Old San Juan in Puerto Rico, begun by Spanish military engineers in 1539 to protect the harbor from naval attack. Built up over more than two centuries into a six-level complex of thick masonry walls, gun batteries and a lighthouse, its layered design let defenders fire on approaching ships from multiple elevations at once, and it withstood attacks by English and Dutch forces in the sixteenth and seventeenth centuries. The fort's walls in places reach roughly twenty feet thick, built from sandstone and coral rock quarried nearby. It forms part of the San Juan National Historic Site and, together with the adjoining city fortifications, was inscribed as a UNESCO World Heritage Site in 1983.