Tower 19 was located at the eastern part of the southern fortress wall and stood at 19.10 m away of both U-shaped towers 18 and 20. It had a rectangular design with external size: length 18.90 m (east – west) and width 10.30 m (north – south) and internal size: length 13.95 m (east – west) and width 7.80 (north – south). The dado was constructed of large limestone blocks with smooth and rusticated faces and was 0.57 m high. In the high areas walls were made of small stone blocks soldered by white mortar and the inside of the walls was filled with stone rubble with ample amount of white mortar poured over (opus implectum). The angles of the tower were rounded for greater resistance against the attacks of the battering rams. Fortress walls were 2.40 m thick. The entrance to the inside of the fortress was located right in the center of the northern side and was 1.95 m wide. Its sides were constructed by large stone blocks with rectangular sides. Both short sides of the tower – eastern and western – held posterns with opening width of 1.40 m in the outside and 1.70 m in the inside. The tower was repaired after a great fire and the eastern postern was blocked up and the threshold of the southern one was raised with 0.60 m. Inside the tower stood two symmetrical stone pillars 3.20 m away from each other. Their size was as follows: length 2.10 m (east – west) and width of 1.50 m (north – south). By the height that had been unearthed so far the pillars were constructed with the opus mixtum technique: 4 rows of stone blocks and above them – a belt of unclear number of brick rows. Pillars served to support an upper floor (floor level of wooden beams) of the defensive tower. At a later period – probably in mid-6th century – to the south of the tower was constructed an external fortress wall which together with the curtain wall of the old southern fortress wall and with the southern wall of rectangular tower 19 shaped a premise with the following size: length 19 m (east – west) and width of 4 m (north – south). The postern at the western side of tower 19 served as entrance to the premise. The structure of the latest walls was significantly rougher than that of the previous walls. It was made of stone blocks and stone rubble with different size soldered with white mortar with admixture of brick pieces. It was probably used as a room for the guards or as a storage place.