after that a German artillery barrage and aerial bombardment started. The Polish artillery was much weaker and was soon forced to retreat towards Białystok. After preparation, the Germans attacked the northern flank of the Polish forces. Two platoons defending several bunkers located to the north of Narew were attacked from three sides by German tanks and infantry. Initially the losses among German infantry were high, but after heavy artillery fire, the commander of the Giełczyn area, First Lieutenant Kiewlicz, was ordered to burn the wooden bridge over Narew and withdraw to Białystok. The remnants of his forces broke through the German encirclement and reached Białystok, where they joined the forces of General Franciszek Kleeberg. At the same time, an assault on the southern part of Polish fortifications became a stalemate. The Polish bunkers lacked adequate anti-tank armament, but were able to rake the German infantry with machine gun fire. However, at 6 o'clock in the evening, the Polish infantry was forced to abandon the trenches and field fortifications and retreat into the bunkers. The German tanks could finally cross the Polish lines and advance towards Tykocin and Zambrów. However, the German infantry was still under heavy fire and was pinned down in the swampy fields in front of the Polish bunkers. Although Raginis was subordinate to Lieutenant Colonel Tadeusz Tabaczyński, commander of the Osowiec fortified area located some 30 kilometres to the north, he could not expect any reinforcements. On September 8, the Marshal of Poland, Edward Rydz-Śmigły, ordered the 135th Infantry Regiment, which constituted the reserves of both Osowiec and Wizna, to be withdrawn to Warsaw. When the order was withdrawn and the unit returned to Osowiec, it was already too late to help the isolated Poles at Wizna. Heavy fighting for each of the now isolated bunkers continued. Several assaults were repelled during the night and in the early morning of September 10. At approximately 11 o'clock, German engineers, with the help of tanks and artillery, finally managed to destroy all but two of the Polish bunkers. Both of them were located in the centre of Strękowa Góra and continued fighting despite having much of the crew wounded or incapacitated and most of their machine guns destroyed. After the war, the Poles insisted that Guderian, in an attempt to end the Polish resistance, threatened the Polish commander that he would shoot the POWs if the remaining forces did