The Early Christian walls of Nicopolis, one of the most important assemblages of fortification architecture in the southern Balkans, are impressive for their size and preserved height of up to twelve meters. They were built by incorporating part of the Roman walls and taking into consideration the Roman urban fabric. The walls, which have a perimeter of about 2072 meters, are trapezoidal in plan and reinforced by towers. The south wall was erected along the south side of the main road that crossed the Roman city from east to west (decumanus maximus), proving that the road continued in use during Early Christian times. The same tactic appears to have been followed on the west wall, which apparently ran along a north-south road (cardo). To the north and east, the new fortifications used the Roman wall, whose height was augmented.
There were a total of 12 towers along the south wall, set at regular intervals of 33 meters: rectangular, semicircular, and polygonal towers alternated with one another in the same order; there was a round tower at the southwest corner and a polygonal one at the southeast corner. In the small oblique part of the south wall that continued until it met the Roman wall on the east side, there was a series of two semicircular towers, a square tower, and a polygonal tower. A different organizational system was followed for the west wall, which has a total of 16 towers: 11 rectangular ones in a row, 2 circular ones at the north and south corners, 2 horseshoe-shaped ones flanking the main west gate, and a circular one on the north side of a postern 184 meters north of the west gate. The distance between towers ranges between 26 and 40 meters.