The most startling memorial to victims of the Holocaust may also be the easiest to miss. Embedded in the sidewalks of more than 20 countries, more than 60,000 Stolpersteine—German for “stumbling stones”—mark the spots where victims last resided before they were forced to leave their homes. The modest, nearly 4-by-4-inch brass blocks, each the size of a single cobblestone, are planted outside the doorways of row houses, bakeries, and coffee houses. Each tells a simple yet chilling story: A person lived here. This is what happened to them.

Here lived Hugo Lippers
Born 1878
Arrested 11/9/1938 — Altstrelitzer prison
Deported 1942 Auschwitz
Murdered

The project is the brainchild of the German artist Gunter Demnig, who first had the idea in the early 1990s as he studied the Nazis' deportation of Sinti and Roma people. His first installations were guerrilla artwork: According to Reuters, Demnig laid his first 41 blocks in Berlin without official approval. The city, however, soon endorsed the idea and granted him permission to install more. Today, Berlin has more than 5000.

Artist Gunter Demnig lays a Stolpersteine outside a residence in Hamburg, Germany in 2012.Patrick Lux, Getty Images

The Stolpersteine are unique in their individuality. Too often, the millions of Holocaust victims are spoken of as a nameless mass. And while the powerful memorials and museums in places such as Berlin and Washington, D.C. are an antidote to that, the Stolpersteine are special—they are decentralized, integrated into everyday life. You can walk down a sidewalk, look down, and suddenly find yourself standing where a person's life changed. History becomes unavoidably present.

That's because, unlike gravestones, the stumbling stones mark an important date between a person’s birth and death: the day that person was forced to abandon his or her home. As a result, not every stumbling stone is dedicated to a person who was murdered. Some plaques commemorate people who fled Europe and survived. Others honor people who were deported but managed to escape. The plaques aim to memorialize the moment a person’s life was irrevocably changed—no matter how it ended.

The ordinariness of the surrounding landscape—a buzzing cafe, a quaint bookstore, a tree-lined street—only heightens that effect. As David Crew writes for Not Even Past, “[Demnig] thought the stones would encourage ordinary citizens to realize that Nazi persecution and terror had begun on their very doorsteps."

Artisan Michael Friedrichs-Friedlaender hammers inscriptions into the brass plaques at the Stolpersteine manufacturing studio in Berlin.Sean Gallup, Getty Images

While Demnig installs every single Stolpersteine himself, he does not work alone. His project, which stretches from Germany to Brazil, relies on the research of hundreds of outside volunteers. Their efforts have not only helped Demnig create a striking memorial, but have also helped historians better document the lives of individuals who will never be forgotten.