The average thickness of the bunker walls was nearly 5 feet (1.5 meters). Ruins of one of the Polish defense bunkers, now a memorial site Wizną 1939 Photo by Hiuppo CC BY 3.0 If broken, an enemy would have access northwards to Warsaw.The construction of the main fortifications began only in April 1939.īy September 1, the Poles had built six heavy bunkers with reinforced concrete domes weighing 8 tons each, two lightweight concrete bunkers, and eight machine gun pillboxes protected by sandbags or earthworks. Four more bunkers were still in the construction stage when the war began. However, this defensive line was poorly fortified. The 5.5 mile (9 km) line of defenses along the high riverbanks passed between the villages of Kołodzieje and Grądy-Woniecko, with Wizna in the center. In addition, the most important road, Łomża–Białystok, passed through Wizna.
