The word ghetto has recently come to mean an area in a town or city which is mostly inhabited by a single ethnic or cultural group. Originally, however, the word meant something much more specific. During the Middle Ages, a 'ghetto' was an area within a city set aside quite clearly for Jews to live in and which they were forbidden to leave. The term was probably first used in Venice, Italy where in 1516 Jews were confined to an area called the Geto Nuovo. Ghettos were a device used by medieval communities to identify and isolate their Jewish populations, making their periodic persecution much easier.

Ghettos were reinvented by the Nazis soon after they invaded Poland on September 1 1939. Vast numbers of Jews came under Nazi rule as they occupied Eastern Europe. By the end of September the conquest of Poland had largely been completed and more than 2 million Jews had come under Nazi control. Reinhard Heydrich, Chief of Security Police, issued a detailed series of instructions which began: "For the time being, the first prerequisite for the final aim is the concentration of the Jews from the countryside into the larger cities."

Although at this point, the "final aim" was not stated, squads of Security Police and others went about systematically clearing the countryside of Jewish communities and transporting them into large cities throughout Poland. These cities were chosen for their size and their nearness to railway transport. Within each chosen city, an area was set aside both for the Jews who already lived there and also the new influx of Jews forced in from the countryside. Often, the ghettos were sealed off from the rest of the city by the construction of a large brick wall. Access both in and out was therefore controlled entirely by the German administrators.

The first Polish ghetto was set up in Piotrovkov Trybunalski in October 1939, followed by Lodz, Warsaw, Lublin, Radom and Lvov. The Vilna ghetto in Lithuania was established following the mass murder of Jews at Ponar, then the Riga ghetto in Latvia, following a similar massacre in the Bikernieki Forest. Other major Polish ghettos included Krakow, Chelm and Kielce.

In Warsaw was the largest Polish ghetto, where 445 000 Jews were forced to live by March 1941. Jews from Austria, Germany, France, Holland and Belgium and other countries were also sent to the Polish and other ghettos. Between 1939 and 1945 the Nazis established 356 ghettos throughout Eastern and Central Europe.