<P> Castillo San Cristóbal, also known as Fort San Cristóbal, is a fort in San Juan, Puerto Rico . It was built by Spain to protect against land based attacks on the city of San Juan . It is part of San Juan National Historic Site . </P> <P> Castillo San Cristóbal is the largest fortification built by the Spanish in the New World . When it was finished in 1783, it covered about 27 acres of land and basically wrapped around the city of San Juan . Entry to the city was sealed by San Cristóbal's double gates . After close to one hundred years of relative peace in the area, part of the fortification (about a third) was demolished in 1897 to help ease the flow of traffic in and out of the walled city . </P> <P> This fortress was built on a hill originally known as the Cerro de la Horca or the Cerro del Quemadero, which was changed to Cerro de San Cristóbal in celebration of the Spanish victories ejecting English and Dutch interlopers from the island of this name in the Lesser Antilles, then forming part of the insular territorial glacis of Puerto Rico . </P> <P> Castillo de San Cristóbal (Fort San Cristóbal) also contains cisterns that were used for the transport of water during the ages of the Spanish Colony . They are extremely large (30ft tall, 60ft wide and 100ft long) and were used as bomb shelters during World War II . They could be used for a future war again with some refurbishments . </P>

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