When the Red Army liberated the Nazi concentration and extermination camp Auschwitz-Birkenau on January 27, 1945, the soldiers encountered unimaginable horrors, including mass graves, the smoldering remains of gas chambers and prisoners starving to death.

The solemn commemoration came amid a worldwide spike in antisemitism and new surveys suggesting basic knowledge of the Holocaust is eroding.

Watch live as Holocaust survivors return to Auschwitz in Poland on Monday, 27 January, marking 80 years since the concentration camp was liberated. Holocaust Memorial Day is held yearly on 27 January to commemorate the memory of the six million Jews and other groups who the Nazis murdered in the Holocaust.