The fortress is located in the Bilgorod-Dnistrovsk city (Odesa region). It was built on the remains of the Greek city Thira that existed until the 4th century. The fortress was allegedly built in the 13th century to control the Dnister estuary. The Citadel (four large towers, connected by a powerful wall) forms the basis of the fortress complex. The inner walls divide the fortress into several courtyards that could serve as be separate fortifications.The peculiarity of the fortress is the cores of the wall, the so-called tetraksys, a figure with 10 points, that form 9 equal right triangles. Supposedly, it is a magical figure because a similar symbol has been used by the Druids. In 1832 the fortress lost its strategic importance, and in 1896 it was declared as a historical and architectural monument.