On a cruise to San Juan, Puerto Rico, we saw one of several citadels, that once protected the Caribbean Island. Spain built these huge citadels to protect the harbor of San Juan and the city.
These citadels were built on a cliff high above the ocean. It had very thick walls. Thick sea walls were built along the water.
It was a beautiful sight coming toward the harbor and seeing the massive fortifications up above. It would have been intimidating for a ship in olden times if they came with the intentions of attacking the island.