The Antiguo Cuartel Militar Español de Ponce or "El Castillo" (English: Old Spanish Military Headquarters in Ponce or "The Castle") is the only structure directly related to the events of the land defense of Puerto Rico during the 1898 American invasion of the Island. The historic building dates from 1894 and is located on Calle Castillo in Ponce, Puerto Rico, in the city's historic district. The structure was listed on the U.S. National Register of Historic Places on 14 May 1987.