More than one million people, mostly Jews, were killed at Auschwitz-Birkenau, Nazi Germany's largest concentration camp in occupied Poland, between 1940 and 1945.
A group of survivors will take part in a ceremony marking the 75th year since the Soviet army liberated it from the Nazis, but that number is dwindling year after year.
The survivors' message is clear - that the world should not allow this to happen again.
Al Jazeera's Jonah Hull reports from the Auschwitz-Birkenau concentration camp, Poland.
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