Petrich Kale Fortress

Petrich Kale is a historically significant Early Byzantine and medieval Bulgarian fortress east of Razdelna in Varna Province. It stands on a high stone terrace within the Avren Plateau and forms part of an important Early Byzantine defensive system.
The fortress was built in the fifth–sixth century and was a key element of this defensive line. During the First Bulgarian Empire it is thought to have ceased functioning as a military installation, with Slavic settlements developing in its place. In 1154 the Arab traveller and geographer Muhammad al-Idrisi described Petrich Kale as a "large, beautiful and wealthy town". During the Second Bulgarian Empire it enjoyed renewed prosperity and became an important defensive position.
In 1388 Petrich Kale fell under Ottoman rule. In 1444, during the Crusade of Varna, crusader forces advanced towards the stronghold. The fighting involved the collapse of sections of the walls and penetration into the fortress.
The stronghold was studied in the twentieth century, with research focusing on various aspects of its life and structure. Excavations in 2006 uncovered the remains of a Roman military headquarters, a staircase approximately twenty metres long, water reservoirs and artefacts including arrows, coins and iron objects. The search for finds and discoveries continued into the second decade of the twentieth century.
The remains of Petrich Kale include two surviving towers measuring eleven by nine metres, fifty metres apart and rising to seven metres. The fortress has a triple circuit of walls covering the western and northern sides and parts of the eastern and southern sides. The rock formation on which it stands protects the eastern and northern approaches, with access possible only from the south along a narrow rocky strip linking it to the Avren Plateau. Remains of a wall, dwellings from the eleventh–twelfth century, a small single-nave church and graves around it have been found within the fortress. A particularly impressive feature is the rock-cut staircase, approximately twenty metres long, leading to two enormous water reservoirs with a capacity exceeding 700 cubic metres.