The Petrus Fortress is located on Mount Čokoća, at an altitude of 314 meters. Archaeological research of the fortification was conducted in two phases, from 1980–1981 and 2004–2005. With a base length of 297 meters, Petrus ranks among the largest hilltop fortifications in Serbia. The city walls, built from roughly cut and irregular stones with lime mortar, are 2.40 meters thick and preserved to heights ranging from 1.5 to 7 meters. The interior of the fortress is organized into two parts: the citadel and the large town. The citadel, located on the western plateau, measures 62m x 36m. Numerous fragments of ceramics, stone sculptures, and frescoes were discovered within it.

Based on the construction techniques and discovered artifacts, four chronological phases of the fortification have been identified. The most recent phase includes walls built in an irregular technique, dated to the 14th–15th centuries, which rest on walls constructed in a regular technique with leveling courses of bricks between every second row of stones, dated to the 12th century. At a lower elevation, a wall built in dry stone technique from the 6th century was discovered, which is founded on a cultural layer from the Early Iron Age.

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