Mass graves from Soviet mass executions
In July 2010, a mass grave was discovered next to the Peter and Paul Fortress in St. Petersburg, containing the corpses of 80 military officers executed during the Red Terror of 1918–1921. By 2013 a total of 156 bodies had been found in the same location. At about the same time a mass grave from the Stalin period was discovered at the other end of the country in Vladivostok. These and later mass graves in the Soviet Union were used to conceal the large numbers of Soviet citizens and foreigners executed by the Bolshevik  regime under Vladimir Lenin and Joseph Stalin. Indiscriminate mass killings began in January 1918 during the Russian Civil War (1918-1922) as the Bolsheviks launched their Red Terror. After the upheavals of the First Five-Year Plan (1928-1932) the killings reached a peak in the Great Terror of 1937–1938. At all times they were directed and carried out by the Soviet secret police under its changing titles: the Cheka during the Civil War, the OGPU during forced collectivisation of agriculture, and the NKVD during the Great Terror. Mass murder, 1937-1938. In the final years of the USSR and  after its demise in 1991, killing fields and burial sites were uncovered and memorialised across the countries of the former Soviet Union. Some dated back to the Civil War or to the intervening years when the secret police in all major Soviet cities regularly used unmarked graves in existing cemeteries to dispose of those they executed or killed during interrogation. Most came into existence during the Great Terror. Between 5 August 1937 and 17 November 1938 the scale of killing reached its apogee. In a series of 12 "operations" the NKVD executed at least 680,000 men and women. That is  the documented total: the real figure is almost certainly higher. In preparation for mass murder on such a scale the NKVD People's Commissar Yezhov instructed his subordinates throughout the Soviet Union to identify areas not far from the major urban centres where thousands of bodies could be quickly concealed. This was described by the late Arseny Roginsky “In July that year NKVD departments across the USSR had already begun to set aside special ‘zones’, areas for the mass burial of those they shot. For locals these usually became known, euphemistically, as army firing ranges. This was how the zones  that we know today came into being: the Levashovo Wasteland near Leningrad, Kuropaty near Minsk, the Golden Hill near Chelyabinsk, Bykovnya on the outskirts of Kiev, and many others.” The widespread description of these sites as "firing ranges" has led to a confusion between killing fields where the victims were both shot and buried, e.g. Sandarmokh, and the many other sites where those being buried and concealed had already been executed elsewhere. Russian Federation. Northwest Russia In or near Moscow Siberia 1940 onwards. The Katyn massacre in Russia. With Stalin's approval, NKVD chief Lavrenty Beria issued orders to shoot  25,700 Polish "nationalists and counter-revolutionaries", Poles held captive in a number of internment camps in western Russia, on date. The executions are collectively known as the Katyn massacre but they took place in three distinct locations: Katyn (Smolensk Region), Tver in central Russia and Kharkiv in eastern Ukraine. At Katyn (Smolensk Region) at a site used earlier for executing hundreds of Soviet citizens. Polish POWs were shot there by the NKVD in April and May 1940. 4,413 bodies were later exhumed and identified. Polish prisoners were also shot at Kharkiv in eastern Ukraine and in Tver, then known as  Kalinin. Some of them were buried at Mednoe, today a commemorative site in the Tver Region, having first been shot in Tver.