The Great Memorial Cross passes the Moscow Kremlin on 6 August
It was taken by boat from the Solovetsky Islands, site of a prison camp, and will be erected at a former execution ground outside the capital.
An estimated 20,000 people, 1,000 of them Christians, were executed at the Butovo range between 1937 and 1938.
The Siberian cedar cross is 12.5m (41 feet) high and 7.6 (25 feet) wide.
researcher at the Russian human rights organisation Memorial
Its journey from the islands began on 25 June and part of its route followed the White Sea Canal, a Stalinist construction project which claimed the lives of thousands of convicts.
It was constructed at the Solovetsky Monastery over six months.
Russian human rights activists fear that the Gulag and Stalin's crimes are not being properly commemorated by the Russian authorities, and the memory of the victims may be lost to future generations.
"There's a new regime that wants heroes, not victims," Tatyana Voronina, a researcher at the human rights organisation Memorial, told AFP news agency."They prefer to celebrate the victory in World War II. It doesn't make you feel proud when you know that it's your own people who did this."