Sarny Fortified Area (known in Polish in several names: Sarneński Rejon Umocniony, Sarneński Odcinek Umocniony, Bastion Polesie) was a line of bunkers and trenches along both sides of the Sluch river, in the area of the town of Sarny, northern Volhynia in Ukraine. In the interbellum period Sarny belonged to the Second Polish Republic, it was located close to the border with the Soviet Union. As Polish military authorities regarded the Soviets as the main threat (see: Plan Wschod), in 1936 construction of fortifications began. It was planned to be fully operational in the spring of 1940. Total length of the defence works was some 170 kilometers, number of objects - 358.