Approaching from the west, Portobelo's first fort is Fuerte Santiago. Built after Vernon’s attack, some walls were 3m thick, made entirely of cut coral. Known to the Spaniards as ‘reef rock,’ coral was a popular building material since it’s easily shaped, tough as granite yet light as pumice. Ruins include officers’ quarters, artillery sheds, a sentry box, barracks and watchtowers.
After mudslides, some coral walls had to be replaced with concrete reinforcements.