In September of 1939, shortly after the German invasion of Poland, Reinhard Heydrich ordered the segregation of Jews in Warsaw. The first Jewish ghetto was established a few days later in Piotrków Trybunalski—the first of more than 1,000 to be established in German-occupied territories.

Conditions in the ghettos were abysmal. The areas were surrounded by high walls, with nobody allowed in or out without a permit. Overcrowding and lack of resources led to hunger and starvation, poor sanitation, and wildfire-fast spread of disease. (For a little perspective: The Warsaw Ghetto, the largest one established, held roughly 450,000 Jewish people within about 1.3 square miles.) What’s more, the winter months brought freezing conditions with little or no access to heat. Numbers vary, but it is estimated that anywhere from tens of thousands to upward of half a million people died in the ghettos.

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