Solovetski or Solovetsky Islands (sələvyĕtˈskē) [key], archipelago, c.150 sq mi (390 sq km), N European Russia, in the White Sea at the entrance of Onega Bay. A monastery, built in the first half of the 15th cent., is on the largest island. It was used as a military fortress against Sweden in the 16th and 17th cent., and the early settlement and economic development of the Karelo-Murmansk area was from there. From the reign of Ivan IV until 1956 the islands were a dreaded place of exile for criminals and for political and religious prisoners; during Soviet rule, some 40,000 prisoners died (1923–39) there. Solovetski forced-labor camps produced lumber, peat, and building stone. The islands were declared a natural and historical preserve in 1974.