The names of thousands of people who were executed during the bloodiest period of Stalin’s purges were read aloud in a daylong ceremony here on Monday at a square in front of the former Soviet secret police headquarters, where many of the victims died or began their journey to execution.

Memorial, a human rights organization that assists survivors of Soviet repression and commemorates its victims, organized the event, one of a series this year marking the 70th anniversary of a period known as the Great Terror, when executions became a daily event.

The organization estimates that an average of 1,000 people a day were executed during the Great Terror in 1937 and 1938, and that a total of 12.5 million people were victims of political repression during the Soviet era.