Castillo de San Cristóbal ( Puerto Rico ) The Castillo de San Cristóbal is a Spanish 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 . Castillo de 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 gate s . 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 . 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 . La Garita del Diablo . Most of San Juan ' s fortified walls have guerite s ( sentry boxes , " garitas " to the locals ) at various points . One of the guerites at Fort San Cristóbal is called " The Devil ' s Guerite " ( " La Garita del Diablo " ) . This guerites offer a vantage point to watchmen guarding the sea shore , while protecting them . This particular guerite is one of the oldest parts of the fort being built in 1634 . There are several legends surrounding the guerite . Some of them say that soldiers disappeared randomly from the guerite . However , it is mostly believed - and told so in various local stories - that the only soldier that apparently disappeared was a soldier called Sánchez , who fled his post to escape with his girlfriend , called Dina . However , the legend still surrounds the guerite and most people ask for it when visiting the fort . Although it is currently inaccessible to the general public , it can be seen from the upper part of the fort . Historical timeline . 1521 - San Juan founded by Spanish settlers from Caparra . 1539 - Construction of the first fortified defenses at Castillo San Felipe del Morro and La Fortaleza , with batteries aimed at the harbor entrance . 1595 - The English attack San Juan , led by Sir Francis Drake , 25 ships penetrated the line of fire from El Morro . At the end of the battle the English fled taking some prisoners but no treasure , the reason for which they attacked . 1598 - The English attacked a second time San Juan , this time led by George Clifford who wanted to clean England ' s honor which had been " dirtied " by Sir Francis Drake ' s defeat , he organized the greatest squadron ever put together by the English against Spain . The first battle resulted in a Spanish victory , but the exhausted Spanish troops couldn ' t impede the English entry into San Juan . But after a hard resistance by the Spaniards and a sudden digestive epidemic that almost destroyed the English troops they retreated , leaving the island of Puerto Rico under Spanish rule once again . 1625 - The Dutch attack and take San Juan from the land side . Construction of some form of defense for San Cristóbal Hill ordered to prevent other attacks from the land side . 1634 - A small redoubt is built on the high ground known as San Cristóbal on the northeast side of San Juan . 1765 - 1783 - Main period of construction of San Cristóbal as we see it today under the directions of Royal Engineers Tomás O ’ Daly and Juan Mestre . 1787 - An earthquake damages the structure of both San Felipe del Morro and San Cristóbal . 1797 - San Cristóbal helps repel the attack on San Juan from the land side by a British invasion force of 7 , 000 - 13 , 000 men commanded by Sir Ralph Abercromby . Abercromby ' s forces , one of the largest ever to invade Spanish territories in America , are halted a mile from San Cristóbal at the Escambrón defenses , also known as San Juan ' s First Line of Defense ; see Fortín de San Gerónimo . 1824 - María de las Mercedes Barbudo , a political activist who was the first female from Puerto Rico " Independentista " , meaning that she was the first Puerto Rican woman to become an avid advocate of Puerto Rican Independence , and who joined forces with the Venezuelan government , under the leadership of Simon Bolivar , to lead an insurrection against the Spanish colonial forces in Puerto Rico . , was held captive in the fort pending her exile to Cuba . 1855 - Mutiny by the San Cristóbal artillery brigade against the Spanish crown . The Castillo is held by rebels for 24 hours causing panic in the city when the cannons are turned around and aimed at the city . 1897 - A large segment of 18th century walls are dynamited from San Cristóbal to the harbor docks to allow San Juan to expand . 1898 - On 10 May 1898 , the first shot which marked Puerto Rico ' s entry into the Spanish - American War was ordered by Captain Ángel Rivero Méndez is against the USS " Yale " from Castillo San Cristóbal ' s cannon batteries . San Cristóbal ' s gunners duel with US Navy warships during a day long bombardment 10 May 1898 . Six months later Puerto Rico becomes US territory by terms of the Treaty of Paris which ends the Spanish - American War . 1942 - Still an active military base when World War II breaks out , concrete pillboxes and an underground bunker control center are added to the ancient defenses of the Castillo San Cristóbal . 1949 - San Juan National Historic Site is established as the most impressive structure in the new world . 1961 - The US Army moves out of the forts of Old San Juan , and they become the jurisdiction of the United States National Park Service , to be preserved solely as museums . 1983 - San Juan National Historic Site is declared a World Heritage Site by the United Nations . Fort San Cristóbal in popular culture . Fort San Cristóbal was used to film the Wizard Battle for the between Justin and Alex ( David Henrie and Selena Gomez ) . The director and crew filmed here for three days and found a few fragments from 16th century pots . For this reason they needed archaeologists with them at all times whilst digging for the special effects . Also , the fort posed as a Spanish castle in Cadiz for the film " " .