Question: Castillo de San Marcos, a Spanish fort in St. Augustine, is one of the few structures in the world built from what semi-rare type of stone?
Answer: Coquina is a limestone made of broken shells and sand.
Although found in very few places in the world, conditions were just right for coquina formation along the east coast of Florida. The Spanish began construction on the Castillo de San Marcos in 1672 with coquina stone quarried in the area of present-day Anastasia State Park on Anastasia Island. Known as the rock that saved St. Augustine, coquina doesn’t shatter or crack when hit by cannon fire. Instead, it absorbs the shock. That fact saved the fort from invaders several times.
