"Arbeit macht frei" was and is usually found on a sign on top of gates the concentration camps, since they typically were forced to perform labor under horrid conditions. The most infamous one with a sign was called Auschwitz. Originally used for prisoner of war from Poland, the nazi soon built Auschwitz II-Birkenau in 1942 where 700 people could simultaneously killed but you would be locked up on the killing chamber for up to a week, with no food and water, until it was "worth it" to kill enough people at once...