Seeking to calm the furor, Mayor Alexandr Rogachuk of Brest told local journalists last month that the city, the scene of ferocious fighting in both world wars and earlier conflicts, had been built atop the unmarked graves of countless unknown war victims.

“Everyone here is a sinner in this respect,” he said. “We are all walking on bodies,” While it was known that the building site might contain “a few dozen” bodies, the mayor said, “nobody expected such a large number.”

Jews made up about half Brest’s population of around 60,000 in 1941, and were thought to have been killed mostly in a secluded forest 70 miles east. They had been taken there by rail in an early test of logistics for Hitler’s “Final Solution.”

Evgeny Rosenblat, a historian who has studied the murder of the city’s Jews during World War II, said it had long been known that the Nazis also carried out massacres in the center of Brest. Still, he said, he was surprised by the large number of remains found on the building site. Just how and when those people died are not known, as few witnesses survived.