Wizna is known as the Polish Thermopylae. It was a place of the Battle of Wizna (September 7–10, 1939) during the initial stages of the German Invasion of Poland. The Polish defense force consisted of approximately 700 soldiers and 20 officers armed with 6 pieces of heavy artillery. They held a fortified territory against a vastly larger invading force at great cost of lives, before being annihilated with no known survivors. Heavy German assault on Polish bunkers continued for three days and was successfully repelled until the early morning of September 10. The German engineers with the help of tanks and explosives managed to destroy all but two Polish bunkers. Both of them were located in the centre of Góra Strękowa, and despite having much of the crew wounded or incapacitated and most of the machine guns destroyed continued their resistance till the end. It is said that General Heinz Guderian threatened the Polish commander, Captain Władysław Raginis, that he would shoot the POWs if the remaining force did not surrender. The symbol of Polish will, Władysław Raginis, committed honorable suicide by throwing himself on a grenade. German losses are not known. In his diaries Heinz Guderian noted that 900 German soldiers were killed in action, although that number is probably underrated. It is certain, however, that the Wehrmacht lost at least 10 tanks and several other AFVs in the struggle.