The Castillo de San Cristóbal is a Spanish fort in San Juan, Puerto Rico. It was built by the Spaniards 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, basically wrapping the city of San Juan. Entry to the city was sealed by San Cristóbal's double gates.