Remains of the Svac fortification are situated on a rock above Šasko Lake, northeast of Ulcinj, near the village of Šas.

Svac used to be an Episcopal town already in the 8th century. There are no data concerning its development in the early Middle Ages. A biography of Nemanja, from 1216, mentions it as the town he conquered on the coast. In 1241, the Mongols destroyed Svac and killed its inhabitants, however, the town managed to recover after this incident. From the late 14th century onwards, it started to decline; in 1406, it was referred to as a village and its episcope made a plea to Venice to reinforce and encircle the settlement with walls the way it had been before. The town minted its own money.

The Svac fortification was encircled by walls containing towers. The south side was naturally inaccessible owing to cliffs descending steeply to the lake. On that side there is a path leading to the lake, with traces of a gate by it. The fortification was accessed from a suburb, on the north. Next to the entrance gate, the Cathedral of St. John is situated, built in 1300, according to the inscription on the facade. Judging by the fragments inserted into the western wall, it is possible that an older church had existed on the site, probably destroyed by the Mongols. The church apse was inserted in the ground level of an older tower, of which a storey has survived. Besides the Church of St. John, remains of another small church are found within the north town wall, as well as of one outside the wall. In the town itself, there are remains of residential buildings, some of which have been preserved quite well. Since the town was abandoned already in the 15th century, we can positively date all its parts into the Middle Ages.

North of the fortification, remains of a suburb can be traced among the ruins of eight churches of Svac . In the suburb, the most dominant is the Church of St. Mary, probably built after 1300.