The Fortress of San Jerónimo del Boquerón is a small fort located at the mouth of the Condado Lagoon, across from the historic sector of Miramar in San Juan. It was built during the 18th century to replace a smaller battery (called El Boquerón) that stood at the easternmost end of the San Juan islet. The original Boquerón battery was used by the Spanish to defend the city of San Juan from attacks by Sir Francis Drake in 1595 and George Clifford, the third Earl of Cumberland in 1598, who managed to destroy it during his attack. San Jerónimo became part of San Juan's first line of defense, along with the San Antonio Fort/Bridge and Escambrón Fort, being the fourth and last line of defense the formidable Castillo San Cristóbal, which guarded the city entrance proper.