Bjni Fortress is located on the eastern side of the village of Bjni, Kotayk province, on a rocky promontory on the right bank of the Hrazdan river. The fortress is divided into two main sections — the Great (Upper) Fortress and the Lower Fortress. In the upper section are the foundations of the Surb Khach (Holy Cross) church, a 10th-century reservoir, and the remains of a civil structure; in the Lower Fortress are a 10th-century secret passage and multi-layered residential and production structures dated to the 10th–17th centuries.
The history of the medieval fortress of Bjni has been linked, from the 10th century, to the princely house of Pahlavuni. They rebuilt an earlier fortification and made it their princely seat, a fortress-town. In the 11th century Bjni was among the domains of Grigor Magistros Pahlavuni. After the fall of the Bagratuni kingdom, in 1045, Grigor Magistros ceded Bjni, along with his other domains, to Byzantium, in exchange for estates received in Mesopotamia.
In the north, sections of a pyramidal (buttressed) wall about 120 m long have survived; the main gate was also located here.
In 2007–2008, sections of the walls, secular buildings, and churches, as well as the reservoir and the beginning of the underground passage, were reinforced and restored.
In the early 13th century Bjni passed to the Zakarids, and at the end of the 14th century it suffered the invasions of Tamerlane (Lenk Temur).
