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, basically wrapping 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.
Most of San Juan's fortified walls have guerites (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 particular guerite is one of the oldest parts of the fort being built in 1634.
Legend says 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 did so to escape with his girlfriend. However, the legend still surrounds the guerite and most people ask for it when visiting the fort.
1521 - San Juan founded by Spanish settlers from Caparra.
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. 's M1902 Officer's Saber (Sword) and Scabbard at the National Historic Trust site at San Cristobal</small>]] 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.
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.
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 May 10, 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 May 12, 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.