A Brief History of El Morro
The city of Old San Juan was founded in 1521 by Spanish settlers. The first fortification, La Fortaleza (The Fortress), began construction in 1533 and currently serves as the governor's mansion. Castillo San Felipe del Morro, or El Morro for short, was the second fort built on the islet of what is now Old San Juan and Puerta de Tierra. El Morro's construction commenced in 1539 and finished in 1790; during those 250 years El Morro went from a promontory mounted with a cannon to a six-level fortress designed to unnerve attackers approaching from sea.
A half mile across the mouth of the Bay of San Juan is another smaller fort called Fortín San Juan de la Cruz, known as El Cañuelo. When enemy ships would try to enter the bay, the two forts created a crossfire that effectively closed the entrance to the bay and the rest of San Juan. Thanks to El Morro (and El Cañuelo), the Spanish were able to defend Puerto Rico from invasions by the British and Dutch, as well as pirates.
In 1898, as a result of the Spanish-American War, the island changed hands from Spain to the United States. El Morro was designated as part of Fort Brooke and actively used as a military installation during the First and Second World Wars.
In 1961, the US Army retired El Morro, passing it on to the National Park Service to establish as a museum. And in 1983, El Morro and the walled-city of Old San Juan were declared Unesco World Heritage Sites.