The ancient fortresses on the south side of the old port of Dubrovnik were, at one time, separate structures. Along with the monumental walls that surround the city, St. John's Fortress provided protection from invaders intent on taking the town.
Sometime in the 16th century, all bastions around the city were merged to provide impenetrable protection of the medieval town. Today, St. John Fortress houses a maritime museum and a public aquarium. If you want to learn all about the seafaring traditions of Croatia, be sure to incorporate a trip to the walls and fortress into your travel plans.