This photo illustrates one of El Morro’s key defenses. The fort was built on Cavannos Ridge, helping to protect it from attack by sea. The name translates to “The Rock.” This position on the 70 foot promontory overlooking the harbor entrance was selected by engineer Battista Antonelli. He left a cornerstone here dated September 20, 1589, marking the commencement of the castle’s construction. The stone rampart on the left measures 59 feet thick.