when the Thracians, drawn by the natural defence of the place, built a fort. It was used by the Romans and in the 6th century AD was considerably renovated by Byzantine Emperor Justinian to be used as a protection against incursions by barbarians, and mostly by the Slavs. The fortress was additionally fortified in the 9th century, this time around because of the incursion by the Bulgarian army in Byzantine territories.

The fort is mentioned in the late 11th century in the Statutes of the Monastery of Bachkovo, founded in those days. Its founder, Gregory Bakuriani granted the citadel, called Petrich (from the Greek word petros meaning “rock”), to the monas­tery. In 1204, it was conquered by the crusaders only to be taken back a year later by BulgarianKing Kaloyan. The fortress was once again renovated in 1231 under King Ivan Asen II, as evidenced by an extant stone inscription, and for this reason was later called Asenova (Asen's).

Archaeological excavations have unearthed fortified walls, an innermost keep, reservoirs of water, a small church, residential rooms, etc. The innermost keep or donjon was built on the hilltop. In peacetime it was the governor’s residence and in days of war it was used for defence and as a watchtower. The two reservoirs of water were built in the most well-protected part of the fort to collect rainwater.

The well-preserved 13th-century “Holy Virgin of Petrich” Church is the landmark of the site. It was among the earliest across the Orthodox Christendom with a tower used both as a belfry and