Servia, as a fortified Byzantine settlement, was part of a broader system of defense, which was extended throughout the Byzantine Empire in the 6th century AD under Emperor Justinian to strengthen its borders. The castle has an irregular shape following the geophysical configuration of the steep rock on which it is built. It is divided into three unequal parts: the citadel at the highest point (2,5 hectares), the upper city (20 hectares), and the lower city at the foot of the hill (75 hectares). This layout is defined by three rows of walls creating successive levels of defense, ensuring maximum protection for the inhabitants during a siege. At the same time, as can be seen from Byzantine sources, this arrangement of the city into three successive zones reflected its social stratification: at the lowest and most populous level, the lower city, were the dwellings of the popular classes, peasants, and workers. The second, the upper city, which was less densely populated, was home to the middle class, the merchants, and officials, while the third level of fortification, the citadel, was home to the ruler. As documented by the sources, a significant part of the population resided outside the walls and sought protection within the walls in the event of a siege.

The largest part of the fortification of the city of Servia has collapsed, and as a result, the outline of the walls is not entirely clear today. Small clusters of ruins are sporadically preserved from the outer enclosure, mostly following the shape of the hill. Many of the wall’s surviving parts stand at a considerable height, partly due to the ground’s steep slope. As for the functional aspect of the walls, there are no clear indications regarding the configuration of the ramparts, while the on-site surface survey did not reveal the existence of an embankment or moat. Sparsely arranged rectangular towers, except for the citadel’s towers, reinforced the castle’s defenses. This proves that the castle’s defenses were based mainly on its strategic position and the defensive advantages of the hill’s geomorphology. In the northeastern part of the city, the ruins of the central gate of the outer wall of Servia can still be seen. A smaller gate tower is visible on the western side of the middle wall.