By Monica Hesse

Washington Post Staff Writer
Thursday, June 4, 2009

A little more than a decade ago, researchers at the U.S. Holocaust Memorial Museum decided to create an encyclopedia of concentration camps. They assumed the finished work would be massive, featuring a staggering 5,000 to 7,000 camps and ghettos.

They underestimated by 15,000.

Their ultimate count of more than 20,000 camps — which they reached after a year of research — is far more than most scholars had known existed and might reshape public understanding of the scope of the Holocaust itself.