Most gas chambers were destroyed by the Nazis in the last months of WWII, as the Soviet troops gained ground, in order to cover their actions. In Auschwitz, one of them was reconstructed after the war, alongside two crematorium ovens.

People selected to die were taken to the entrance of these chambers, were told to undress so they could take a shower, and guided to underground rooms. Once locked inside, Nazi soldiers dropped Zyklon B through openings in the ceiling. Zyklon B is a pesticide that was previously used to disinfest clothing, ships, warehouses, and trains. In Auschwitz-Birkenau, it was used to kill around one million men, women, and children. All of them died in extreme amounts of pain.

The use of Zyklon B became popular because it allowed Nazis to kill thousands of people in just one day. The first experiment with this gas was run in Auschwitz, in the basement of Block 11. A group of Soviet prisoners of war and ill Polish prisoners removed from the camp “hospital” were taken to the block and left there to die. The following day, the SS soldiers realised some prisoners were still alive and increased the dosage.

However, carrying the bodies from Block 11 proved to be a difficult task, and the mass killings were hard to keep in secret. This led the Nazis to build the gas chambers and crematoriums underground, and in houses hidden in the woods. Gas chambers were also operated by prisoners of the camps, who were in charge of carrying and burning the bodies; however, the Zyklon B was always thrown in by SS soldiers.

After the construction of the chambers, the pace of the killings stopped being a problem, as 700 victims could be murdered in just 20 agonising minutes. Getting rid of the dead was the new challenge, and the only thing stopping them from killing faster.