[1] 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.

[3] 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".

[4][5] 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.

The 9 kilometres (5.6 mi) long line of Polish defences stretched between the villages of Kołodzieje and Grądy-Woniecko, with Wizna in the centre.

[6] Units defending the line were subordinate to the Polish Independent Operational Group Narew shielding Łomża and providing defence of the northern approach to Warsaw.

[6] Six bunkers were made of heavy concrete with reinforced steel cupolas weighing 8 tons each, armed with machine guns and anti-tank artillery.

In addition, the area was reinforced with trenches, anti-tank and anti-personnel obstacles, barbed wire lines and land mines.

There were also plans to break the dams on the Biebrza and Narew rivers to flood the area, but the summer of 1939 was one of the driest seasons in Polish history and the water level was too low.

The walls of an average bunker, 1.5 metres thick and reinforced with 20-centimetre-thick steel plates, could withstand a direct hit from even the heaviest guns available to the Wehrmacht at the time.

The Polish defensive line was initially manned by a single battalion from the 71st Infantry Regiment, commanded by Major Jakub Fober.

However, shortly before the outbreak of World War II it was reinforced with a machine gun company from Osowiec Fortress under Captain Władysław Raginis, as well as numerous smaller detachments from a variety of units.

His forces numbered approximately 700 soldiers and NCOs and 20 officers armed with 6 pieces of artillery (75mm), 24 HMGs, 18 machine guns and two Kb ppanc wz.35 anti-tank rifles, with just 20 bullets.

In order to strengthen the morale of his troops, Władysław Raginis and Lieutenant Brykalski swore that they would not leave their post alive and that resistance would continue.

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.

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.

Although all the bunkers were destroyed and the Polish resistance was finally broken, the fortified area of Wizna managed to halt the German advance for three days.