The Battle of Wizna was fought between September 7 and September 10, 1939, between the forces of Poland and Germany during the initial stages of invasion of Poland. According to Polish historian Leszek Moczulski, between 350 and 720 Poles defended a fortified line for three days against more than 40,000 Germans. Although defeat was inevitable, the Polish defence stalled the attacking forces for three days and postponed the encirclement of Independent Operational Group Narew fighting nearby. Eventually the tanks broke through the Polish line and German engineers eliminated all the bunkers one by one. The last bunker surrendered around midday on September 10.