On the edge of a clearing in the Sandarmokh forest, in the Karelia region of northwestern Russia, stands a stone slab carved with this message: “People, do not kill each other.”

It is a memorial to more than 9,000 victims of Stalin’s “Great Terror”, who were shot and buried here by the Soviet dictator’s secret police between 1937 and 1938.

This striking piece of rock also serves as an unofficial monument to the work of the Russian historian who erected it and chose those words chiseled into its surface: Yuri Dmitriev has devoted his life to uncovering the truth of what happened at Sandarmokh, and putting names to these mass executions.

The pine forest beyond is dotted with simple tombstones and homemade memorials, adorned with plastic flowers. Black and white photos of the victims are pinned to the trees. That their descendants have been able to commemorate them in this way is thanks to Dmitriev’s tireless research, together with his colleagues from the Memorial human rights group.