The construction is situated 1625 m southeast of the town of Petrich. Gyaur Kalesi is a fortress, which dated back to the Late Middle Ages- 6th-19th c. It was used as a guard-tower (0,5 – 0,6 hectares in size). The fortress has an elliptic shape and occupies the highest place on a hill with steep slopes to the north, east and west. The fortress from the Middle Ages ( 12th-13th century) was built on the ruins of an ancient fortress from the end of the 4th century. The fortress wall was 1,80 meters wide and surrounds the whole hill. The construction consists of crushed stones cemented together with white and red mortar. A massive pentagonal tower was built from south and a bastion and postern from east.

The fortress was used to protect the road following Struma River on the entrance of the Rupelsko gorge. It also provided control over the valley of the Strumeshnitsa River, the Strumitsa-Melnik road and the turn-off to Thessaloniki. It used to have visual contact with Melnik fortress and with the Kula fortress to the southeast. This was the place to keep an eye on the traffic from the Ograjden Mountain and the south part of the Struma River valley.

The fortress was burnt down in the Middle Ages. Both its name and the fire made scientists believe that there was a fierce battle here, which led to the inclusion of Petrich into the Ottoman Empire. Most probably the name Gyaur Kalesi “a fortress of the Bulgarians” was given by the Ottomans during their invasion of these lands, when this was the main fortress against the invaders.

Nowadays Gyaur Kalesi is a prime element in the coat of arms of the town of Petrich.