Old San Juan’s UNESCO World Heritage Site, the fort known as San Felipe del Morro, was named in honor of King Phillip II and is commonly known as El Morro. It is the largest fortification in the Caribbean. The construction of the Castillo San Felipe del Morro began in 1540 when King Charles V of Spain authorized its construction, which was completed in 1589. Most of the walls in the fort today were added later, in the late eighteenth century. It fell in battle only once, in 1598, to a land assault by forces led by the Earl of Cumberland.