You first notice them almost by accident, as the sun catches the pavement and something glitters underfoot. Yet once you’ve spotted your first Stolperstein (stolpersteine.de) – the name means, literally “stumbling block”, you’ll keep stumbling over more. The little brass plaques, memorials to individual victims of the Nazis, usually stand in front of the house from which that victim was taken, and are the work of Gunter Demnig, a Berlin-born but Cologne-based artist. Since 1996 he’s laid 30,000 Stolpersteine in Germany and others in Poland, Austria, Hungary, the Czech Republic and the Netherlands among other places. They are particularly thick on the ground in the Zülpicher Viertel and Belgisches Viertel, close to the Roonstrasse synagogue; you’ll sometimes stumble across a dozen or more in front of a single house. Incredibly moving, they’re the antithesis of the big, official monuments to the Holocaust: they record the name, birth-date and fate – as far as it is known – of an individual. Chillingly, in many cases, the story is the same: deported and verschollen – missing, presumed dead. The placement of the stones outside the homes of the victims means the fate of entire families is often recorded. While many of the individuals remembered by the stones are Jewish, there are also Stolpersteine for political opponents of the regime, for the murdered Sinti and Roma, and for the Nazis’ gay victims.