Bilsk is the largest fortified settlement of the Early Iron Age in Europe. The defensive line of the site consists of a rampart and the moat of more than 30 km length surrounding the area of ca. 5 thousand hectares. Over the years of the exploration of this archaeological site the idea of the time of settlement of certain parts of the archaeological complex, the origin and peculiarities of the creation of grand defensive structures was gradually formed. A special role in the process of their formation and use was played by the Eastern fortification, the fortified walls of which existed for more than two centuries. Recent exploration of its rampart and moat taking into account the results obtained last years suggest the creation of strong defencive system on the place of unfortified settlements and offered new vision of the appearance of fortified walls.
The analysis of excavation materials of different years allows us to state that the territories occupied by unfortified settlements in the pre-fortress period were much larger and went beyond the future line of wood-earth fortifications. For more than a century and a half in the western part of the settlement complex there were no defencive structures. Only open settlements are known, which appeared in the last third of the 8th century BC. The situation changed in the second half of 6th century BC when the eastern part of the complex was occupied by the population with other traditions. Probably at the beginning of the third quarter of the 6th century BC the founders of the settlement, located in the eastern part of the watershed plateau, surrounded the most important part of the village with a wooden fence (a wall of logs, or mud). A similar wall defended the settlements within the modern Western settlement. The defensive line of the Great Fortress was later planned according to the same principle. We believe that such a light fence, without additional engineering structures, had no defensive significance but determined its own social space of settlements, which housed the estates of local tribal leaders, the most important public buildings and other facilities. Probably belonging to the different tribal groups prompted the inhabitants of the two settlements to strengthen the system of defence and surround the perimeter of each of them with an earthen rampart. The settlements gradually turned into a kind of residence of the local elite. We can assume that in the last third of the 5th century BC or at the beginning of the last quarter of this century, most likely, in the unstable situation in the region, the single strong defensive line in the form of an earthen rampart with a wooden wall on the ridge and a moat in front of them was created. The rampart and moat of the Great Fortress probably delineated the boundaries of the centre of the tribal union. The representatives of different ethnic groups and different social groups lived in this large area. The created defensive line with a length of 35 km was relevant until the middle of the 5th century BC until the time of the appearance of the settlement within the Western settlement. In the Eastern settlement life continues for another century and a half, until the endof the 4th century BC.
