At the end of the rail track that delivered more than a million Jews and other people to their deaths in the gas chambers of Auschwitz-Birkenau is a forbidding stone memorial above 19 plaques in 19 different languages, all bearing this message:

“Forever let this place be a cry of despair and a warning to humanity where the Nazis murdered about one and a half million men, women and children, mainly Jews, from various countries of Europe.”

I had joined a guided tour of the Nazis’ largest extermination camp, and by this point the horror of the place was crushing.

On either side of me were the ruins of the two largest gas chambers with their attached crematoria, and the pits where they dumped the ashes. Auschwitz-Birkenau is actually two separate camps, and the tour began with several hours in the claustrophobic barracks and dungeons of the original concentration camp. Some of the barrack rooms have been turned into shrine-like exhibits of the belongings the Nazis stole from each family once they had stepped off the trains. Most disturbing of all is a room filled with mounds of human hair, cropped from each victim for use in stuffing mattresses and pillows. Here and there, little girls’ ponytails poke out from the mass.