The study reviewed the fortification and cultural stratigraphy of the Klyuchi Stone Fortress located in the mountain taiga of the North-Eastern Primorye. The authors elaborated on the history of exploration, geographical location and the relief of the fortress, the spatial structure and the metric data of the fortification facilities. The researchers distinguished three layers of the fortifications and two residential areas and developed the periodization of the settling of the monument. Based on the analysis of the archeological remains, the authors concluded that the fortress was constructed during the initial period of the Bohai state. The summarized information on the medieval hill forts in the Dzhigitovka valley allowed one to present cultural and chronological as well as historical and geographical interpretation of the fortress functioning in details. In the authors’ opinion, the object under review was a part of the Bohai fortification system of the Dzhigitovka River. This system was an important element which covered a large area of the medieval transport network of the region, i.e. an overland road lying along the Dzhigitovka valley to the coast of the Sea of Japan, and the marine highway leading to the north Tatar Strait, Sakhalin Island, and the northern islands of the Japanese archipelago.