San Critobal is the largest Spanish fort built in the New World. It is part of the defensive system for San Juan started about 1539.

Castillo San Cristobal was an important fortification for Spain, and the Spanish Empire used it primarily to protect from land-based attacks for over 250 years. In the 17th and 18th centuries, Castillo San Cristobal was often called the "Gibraltar of the West Indies".