Asen's fortress is the most attractive and frequently visited tourist landmark around Asenovgrad. It is three kilometers away south of the city, on a rocky peak on the left coast of the Asenica River. Next to it leads a panoramic road, diverging at the very beginning of the road Asenovgrad - Smolyan.

The natural rock massif on which the fortress is located has an area of twelve acres. With its almost vertical, even overhanging slopes, it is inaccessible from its three sides. The strategic location and the natural protection of the area were used during the Thracians, which in the fifth century BC build a fortification.

The fortress was renewed during the Roman Emperor Justinian as one of the 300 strongholds prepared for protection by Slavic tribes entering the Empire. Asen's fortress has three large construction periods - in the 9th, 11th and 13th centuries.

The tower, built by the Byzantines, has grown over time, with the villages of Stenimachos and Petrich being formed around it. Its strategic location at the beginning of a passage that connects Thrace with Northern Greece and the Aegean Sea and that it was in a rich agricultural area gradually transformed the Petrich fortress (as it was then called) into a stand-alone business center with its own army, military power.