On the western side of the old town of Bari is the castle, originally a Byzantine-Roman building, rebuilt by Frederick II in 1233 in the Norman Swabian style. Bona Sforza turned it into a palace in the 16th century, adding forts and corner towers over the moat. Later, it was used as a prison and signal station. There are still two towers of the Norman temple. The building now houses an interesting museum with copies of Pauline Norman sculptures and temporary art galleries.