These brass covered blocks are called Stolpersteine (“stumbling blocks”). They can be found in hundreds of cities all over Europe.
The blocks memorialize individual victims of the Nazis. Engraved on the brass are the individual’s name, date of birth, fate, and date of death. It’s then laid flush with the sidewalk in front of the individual’s last freely chosen place of residence.
Stolpersteine is the project of German artist Gunter Demnig. He began with a few blocks in the early 90s. They now number in the thousands.