There were four other death camps in Poland solely for 
  the purpose of killing; Belzec, Chelmno, Sobibor and Treblinka. Apart from a 
  handful of prisoners used to maintain these camps and work in their crematoria, 
  all the others were gassed on arrival. 
There 
  was not enough room to lie down in the barracks, where there were 1200 women. 
  We slept in rows, back to back, with knees pulled up and feet touching. Many 
  of us had dysentry, and climbing over bodies to get out made some women scream, 
  causing the guards to shoot into the barrack. 
   
  Trude Levi, Auschwitz survivor.
Left: 
  There were four gas chambers at Auschwitz-Birkenau, with crematoria similar 
  to this being built here.
  
  Below: The infamous gateway to Birkenau.