Researchers from the United States Holocaust Memorial Museum have concluded that over 40,000 Nazi camps and ghettos existed during Hitler's reign of terror between 1933 to 1945.
The total is far higher than most historians had previously estimated, according to The New York Times.
Geoffrey Megargee and Martin Dean, the lead editors of the project, have compiled the thousands of sites in a multivolume encyclopedia that is being published by the Holocaust Museum. Each volume catalogs thousands of sites, providing a comprehensive history of the "living and working conditions, activities of the Jewish councils, Jewish responses to persecution, demographic changes, and details of the liquidation of the ghettos."
The Holocaust Museum team also created maps of the sites, which were scattered across Europe, and which imprisoned or killed between 15 and 20 million people.
Essentially, this study shows the Holocaust was far more extensive than even historians comprehended.
Hartmut Berghoff, director of the German Historical Institute, said the research is simply astounding, reports The Times.
"We knew before how horrible life in the camps and ghettos was," he said, "but the numbers are unbelievable."