The San Giusto Castle (St. Justin) has been changed several times over the centuries. In the 13th century, the bishops of Trieste/Trst had a palace with a watchtower on the hill. At the time of the Republic of Venice, a fortress was built there. In the second half of the 15th century, Emperor Frederick III of the Habsburg House had a castle built on its ruins. The present image of the castle is the result of rebuilding campaigns conducted by both the Venetians and the Habsburgs. The Austrians had dungeons in the basement.
Nowadays the castle houses the city museum with a collection of medieval weapons. The lookout towers offer views over the whole city, the bay and the surroundings.