Originally constructed by the Romans around 400 AD, it was among the most important castles of the Bulgarian Empire in the Middle Ages before it was partially destroyed by the Ottomans in the 15th century.

Hisarlaka Fortress was the administrative and religious center of the region from the 5th to the 15th centuries.

[2] Bulgarians repaired the fortress extensively in the 6th century after it was destroyed by the Avars and Slavs.

The region of Sliven, in which the fortress lies, was integrated into the First Bulgarian Empire around 705 AD, as part of the new Zagora region, which was populated mainly by Slavs and had been given to the Khan of Bulgaria, Tervel according to his contract with the Byzantine emperor Justinian II.

It remained in use during the time of the Second Bulgarian Empire, serving as in important stronghold in the region.