Hisarlyk ruins are located on the flat part of the hill of the same name, its highest point. Two kilometers away is the Bulgarian town of Kyustendil. The stronghold was built at the turn of 4-5 centuries, it has experienced both the Bulgarian kingdom and was destroyed by the Ottomans in the 15th century.

The fortress was situated on a fortified area of ​​about two hectares, the shape is irregular polygon, which is elongated in the direction from the southeast to the northwest .  The average size of buildings - 175 by 117 meters .  The shape and location of the defensive structure does not coincide with the classical principles of fortification, in this case the structure of the surface configuration to be ground .  On the area of ​​the fortress was located Hisarlyk fourteen towers of different shapes - rectangular, triangular and round, located in different sectors of the fortified walls, four gates and five Poterna - underground passages .  The main gates were oriental, the most extensive, go to the main path .  All underground passages were located very close to the towers of strategic considerations .  Each narrow passage suitable only for walking people, equipped with granite threshold and a horizontal beam to lock the door from the inside .

The width of the outer walls of the fortress Hisarlyk varies from a little over one and a half to three meters, depending on the terrain - in the steep western wall spot is the smallest - only 1, 6 meters. By assumption, archaeologists average wall height of about 10 meters and towers - 12.

The excavations were set different periods of construction of the fortress Hisarlyk that are directly related to the time of its use. Ancient chronicles Procopius of Caesarea left mention of the first and most significant changes under Justinian I, Byzantine emperor, in the 6th century. Incessantly and continuously fortress was used in ancient times and the Middle Ages, as evidenced by a variety of numerous finds at the site of the ruins of fortress.

Hisarlyk Fortress - a monument of architecture and culture, included in the list of objects of national importance.