Morro Castle (môr`ō), fort at the entrance to the harbor of Havana, Cuba. It was erected by the Spanish in 1589 to protect the city from buccaneers. The fort was also used as a prison. Morro Castle was captured by the British under Sir George Pocock in 1762. The fort at the entrance to the harbor of Santiago de Cuba is also called Morro Castle and was built shortly after the Morro Castle of Havana. It was taken by the American forces in the Spanish-American War (1898). Morro Castle on the harbor of San Juan, Puerto Rico, is also a picturesque old Spanish fort.