THE GREAT MOAT - A deep, dry moat separates the core of Castillo de San Cristobal from its outer defenses. The 60 foot depth of the moat would make it extremely difficult for any enemies to scale the walls. The moat also hides the foundations of the fort's walls out of sight and out of reach of enemy cannon fire.   Fort San Cristóbal | El Morro | City Walls | Cañuelo