Prisoner labour at the construction of Belomorkanal, 1931–33. In the early 1930s a drastic tightening of Soviet penal policy caused a significant growth of the prison camp population. During the period of the Great Purge (1937 – 38) mass arrests caused another upsurge in inmate numbers. During these years hundreds of thousands of individuals were arrested and sentenced to long prison terms on the grounds of one of the multiple passages of the notorious Article 58 of the Criminal Codes of the Union republics, which defined punishment for various forms of “counterrevolutionary activities.”
Under NKVD Order № 00447 tens of thousands of GULAG inmates who were accused of “continuing anti-Soviet activity in imprisonment” were executed in 1937-38.
The hypothesis that economic considerations were responsible for mass arrests during the period of Stalinism has been refuted on the grounds of former Soviet archives that have become accessible since the 1990s, although some archival sources also tend to support an economic hypothesis. In any case the development of the camp system followed economic lines. The growth of the camp system coincided with the peak of the Soviet industrialization campaign. Most of the camps established to accommodate the masses of incoming prisoners were assigned distinct economic tasks. These included the exploitation of natural resources and the colonization of remote areas as well as the realization of enormous infrastructural facilities and industrial construction projects.
In 1931–32 the Gulag had approximately 200,000 prisoners in the camps; in 1935 — approximately 800,000 in camps and 300,000 in colonies (annual averages), and in 1939 — about 1.3 millions in camps and 350,000 in colonies. All data about the numbers of prisoners here and below are however taken from documents produced by the NKVD) and are significantly lower than estimates made by historians.