When the Soviet army marched towards Berlin in 1944, thus approaching the concentration and extermination camps, the surviving prisoners were sent on foot to concentration camps in the west of Germany. On these death marches, as they would later come to be known, thousands were shot dead because they were too ill or weak to walk. Others died of undernourishment, illness, and extreme cold. The infamous death march from Auschwitz took place on January 18, 1945, when 58,000 survivors who could still walk were forced to leave the camp to make their way to Wodzislaw Slaski (then Loslau, Germany), several hundred kilometers from there.
Source: Jewish Museum of Deportation and Resistance
See also: US Holocaust Memorial Museum