St. John is a fortress within the city walls of Dubrovnik. It is located on the south side and its main role was to defend the city port.The fort was built in 1346 under the name "Mule Fort". A so-called so- Gundulic's fort was erected nearby according to the designs of the Dubrovnik engineer Pasko Milicevic. Both forts were connected to the towers in 1522, and since 1557 they form the whole as we know it today - a monumental structure partly semicircular in shape. The inside of the fort originally contained a large warehouse of gunpowder. Saint John preserves a considerable part of the cultural treasures of the Republic. It also houses the collections of the Maritime Museum and Aquarium and the Institute for Marine and Coastal Areas. On the terrace serving as the summer stage for the purposes of the Dubrovnik Summer Games, a Triton sailing cannon was housed.