The fortress, (Citadel) known as Onogost, was built in the meridian direction, on the top of the rocky, steep hill, which rose 20-25m above the plain, and was 214m long, and in its middle part, where it is most spacious, was about 30m wide. The west wall, a bit longer, was 1,6m thick, and the east wall, on which leaned the lower part of the fortress, was 1,1m thick. To the south, utmost part of the fortress raised the pentagon tower on three floors, Nebojsa, and at the north the octagon tower.
Castle, the oldest part of the fortress was situated in the middle, and it consisted of two platforms for cannons, the place for sleeping for the two watchmen, and the deep basement, built in the vault which served as a storage for the ammunition. In the west wall, above Pop, beside Nebojsa, the tower without windows and doors was built in, with the basement, in which the severely punished prisoners where put down by the rope. The people called this tower Petkovica, by the Herzegovina chief of the band of haiduks, Petko Kovacevic. At the uppermost part of the fortress was the artillery platform from which 14 cannons could fire in all directions. Two smaller platforms were accustomed, each for one cannon, and at the south and east part of the fortress could be placed 6-8 cannons individually.
The lower town (the part of the fortress at the foot of the hill) was built in the form of a quadrangle. Protected by the fortress, with which it made a totality, and by the three walls, 4m high, and 1,45-1,5m thick, with the towers at the angles and in the middle, it was a little bit narrower than the upper town. The east wall of the Lower town, on whose angles were Proscenia and octagonal tower, with the well, and with the Grand gate in the middle, was 104m long. The south wall was 66m long and the north, 86m. The transport towers were prepared for the infantry defense. The crown of the walls around the lower town passed through the towers and the soldiers could move along it.