This photo was taken at San Cristobal in Old San Juan, Puerto Rico. It is a masterpiece of 18th-century military innovation and engineering. If these walls could talk! But pictures are the next best thing because they tell so many stories in one shot. The fortress of Castillo San Cristobal was strategically built in the mid-1700s by the Spanish. It was named after the saint patron of land travelers, Saint Christopher, and is the largest of fortresses built in the Americas, taking over 150 years to complete. Some additions were made by the US Army during WW11- coastal observation posts and bunkers.