Information: Wikipedia

A Stolperstein literally "stumbling stone", metaphorically a "stumbling block" is a sett-size, 10 by 10 centimetres (3.9 in × 3.9 in) concrete cube bearing a brass plate inscribed with the name and life dates of victims of Nazi extermination or persecution.

The Stolpersteine project, initiated by the German artist Gunter Demnig in 1992, aims to commemorate individuals at exactly the last place of residency—or, sometimes, work—which was freely chosen by the person before he or she fell victim to Nazi terror, euthanasia, eugenics, was deported to a concentration or extermination camp, or escaped persecution by emigration or suicide. As of 29 March 2018, over 67,000 Stolpersteine have been laid in 22 countries, making the Stolpersteine project the world's largest decentralized memorial.

The majority of Stolpersteine commemorate Jewish victims of the Holocaust. Others have been placed for Sinti and Romani people (then also called "gypsies"), homosexuals, the physically or mentally disabled, Jehovah's Witnesses, black people, members of the Communist Party, the Social Democratic Party, and the anti-Nazi Resistance, the Christian opposition (both Protestants and Catholics), and Freemasons, along with International Brigade soldiers in the Spanish Civil War, military deserters, conscientious objectors, escape helpers, capitulators, "habitual criminals", looters, and others charged with treason, military disobedience, or undermining the Nazi military, as well as Allied soldiers.

Abraham Grynbaum was born in Lodz, Poland on 14.03.1925. A student, arrested on 09.06.1943, deported and murdered in Auschwitz.

David Grynbaum was born in Lodz, Poland on 15.03.1927, A student, arrested on 09.06.1943, deported and murdered in Auschwitz.

The family Grynbaum fled together with their children to Uccle in Belgium before 1933. When their father died the brothers Abraham (16) and David (18) Grynbaum were send by the juvenile judge to the Centraal Observatie Gesticht in Mol. Police commissioner Willy Teller refused to register Jewish children from this institution in the so-called Jewish register, but the director of the institution had no objections. 

The Grynbaum brothers were deported to the Dossin barracks in Mechelen on 9 June 1943 and a little later to the Auschwitz where they were murdered.