Military
Castillo San Cristóbal, a vast Spanish fortress on the northern edge of Old San Juan, guarded the land approach to the walled city and became a central part of its defenses. Developed after major attacks in 1598 and 1625, the site began with early works in 1634 and took its full form between 1766 and 1783 under major Spanish military reforms. At its greatest extent it covered about 27 acres, making it the largest fortification Spain built in the New World. It helped repel a British invasion in 1797, saw imprisonment, mutiny, and combat in 1898, remained in military use into World War II, and is now preserved as part of San Juan National Historic Site and a UNESCO World Heritage Site.
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