The southern fortress wall of the Late Antiquity castle of Abritus was 354 m long and had an average width of 2.85 m since in different areas it ranged from 2.40 m with the rectangular towers, to 3.05 m with the southeastern angular tower. The construction technique was like the one used for the other fortress walls: opus implectum. Two fan-shaped angular towers were placed at both ends – the southeastern and the southwestern towers – and at its front stood 2 rectangular towers and 7 U-shaped towers. Of them 1 rectangular and 3 U-shaped towers were placed east of the southern fortress gate and 1 rectangular and 4 U-shaped towers – to the west of it. The average distance between the towers was 19 m. To the east near tower 17 there was a postern in the fortress wall with opening width of 1.25 m from the outside and 1.64 m from the inside. The fan-shaped angular towers protruded from the curtain wall with 6.05 m at the maximum. The two rectangular towers had the following size: length 18.90 m and width of 10.30 m (external) and length of 13.95 m and width of 7.80 m (internal) – with eastern tower 19 and length of 19 m and width of 10.45 m (external) and length of 14 m and width of 8.05 m (internal) – with western tower 23.

The rectangular towers had two massive pillars each sized 2.10 m by 1.50 m and constructed with the technique of opus mixtum (the structure of stone quadrae alternated with belts of 3 and 4 lines of rectangular bricks) that supported the floor of an upper level. Both short walls – eastern and western – of the two rectangular towers had a small door each – posterns with opening widths of 1.25 m to 1.40 m (external) and 1.70 m (internal). The U-shaped towers along the stretch of the southern wall had length of 9.50 m to 10.50 m and width of 8.40 m to 9.45 m (external) and length of 7.80 to 8 m and width of 4.65 m to 4.80 m (internal). The entrances to the towers were 1.60 m – 1.65 m wide. Slightly to the east of the central body of the wall and jutting in from the face of wall and flanked by two U-shaped towers stood the southern fortress wall. Until recently a part of a moat was preserved in front of the western stretch of the southern fortress wall.

The southern fortress wall of Late Antiquity Abritus must have been the most vulnerable part of the defensive system of the castle. This would account for its greater thickness, the additional protection with a moat and the reinforcement of the fortress gate by making it jut in from the face in order to gain additional protection.