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 the invasion of Poland, which marked the beginning of the Second World War in Europe. 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 shelters one by one. The last shelter surrendered around midday on September 10. Because the battle consisted of a small force holding a piece of fortified territory against a vastly larger invasion for three days at great cost before being annihilated, Wizna is sometimes referred to as the "Polish Thermopylae". One of the symbols of the battle is Captain Władysław Raginis, the commanding officer of the Polish force, who swore to hold his position as long as he was alive. When the last two shelters under his command ran out of ammunition, he ordered his men to surrender their arms and committed suicide by detonating a grenade against his neck. History Background Before the war, the area of the village of Wizna was prepared as a fortified line of defence. It was to shield the Polish positions further to the south and guard the crossing of the Narew and Biebrza rivers. The long line of Polish defences stretched between the villages of Kołodzieje and Grądy-Woniecko, with Wizna in the centre. The line ran some from the border with East Prussia, along an elevated banks of Narew and Biebrza rivers. Units defending the line were subordinate to the Polish Independent Operational Group Narew shielding Łomża and providing defence of the northern approach to Warsaw. The Wizna fortified area was one of the most important nodes in Northern Poland, providing cover of both the river crossings, and the roads Łomża–Białystok and roads towards Brześć Litewski on the rear of Polish forces. Construction started in June 1939, only two months before the outbreak of World War II. The spot was chosen carefully; most of the concrete bunkers were built on hills overlooking a swampy Narew River valley. They could be reached either through direct assault through the swamps or by attack