The harbour was the city’s lifeline.
Dubrovnik’s wealth depended on maritime trade, so protecting the Old Port was not a side task. St John formed the southeast defence of the harbour approach and gave the city control over who could enter.
A chain could close the port.
The Dubrovnik Tourist Board describes a chain stretched across the harbour entrance and controlled by a winch from the fortress. It is a small detail that makes the medieval port suddenly feel operational rather than picturesque.
The building still carries the maritime story.
Today the fortress houses the Maritime Museum on upper floors and an Aquarium on the ground floor. That makes the St John area a natural place to continue exploring Dubrovnik’s relationship with the sea after leaving the Walls.
This is also one of the three Walls access points.
An official entrance sits by the Maritime Museum. If your day begins around the Old Port, St John can be a practical alternative to walking across the Old Town to Pile.
Quick answers
What was St John Fortress used for?
It protected the Old Port from the southeast and helped control access to the harbour.
Is there a City Walls entrance at St John?
Yes. The Dubrovnik Tourist Board lists an entrance next to the Maritime Museum at St John Fortress.
What is inside St John Fortress today?
The Tourism Board lists the Aquarium on the ground floor and the Maritime Museum on the first and second floors.
References: Dubrovnik Tourist Board: City Walls and Fortresses