The majority of Jews persecuted by the Nazis shared the experience of being forced to live in a ghetto for a certain period of time. Some of these ghettos existed for several years, others only for a few weeks or even days. While several ghettos were hermetically sealed and surrounded by a wall or a fence, others remained open and were only defined by designating certain streets. According to recent research conducted by the United States Holocaust Memorial Museum (USHMM), there were more than 1100 ghettos in occupied Eastern Europe, among them about 600 on former Polish territory, 130 in the Baltic States and about 250 in the pre-war territories of the Soviet Union.