Radiation monitoring is conducted in nine districts. The radiation background complies with the established radiation situation. The territory of Kaluga Oblast has been inhabited since ancient times. The oldest human sites discovered by archeologists date back to the Mesolithic period (10,000–6,000 BC). The first mentions of Kaluga's towns are associated with events in the 12th century, specifically, the feudal war between the Olegovichi and the Monomakhovichi (Kozelsk - 1146, Serensk - 1147, Vorotynsk -1155, Mosalsk - 1231). In the 14th century, Kaluga lands were the place for constant confrontations between Lithuania and Moscow. Traditionally, it is considered that Kaluga was established as a frontier to protect the Moscow principality from Lithuania's attacks. In 1480–1481, Kaluga's territory was the place of the great stand on the Ugra river, resulting in the liberation of Russian lands from the Tatar yoke and Moscow's transformation into a sovereign state. In the 16th and 17th centuries, with active development of trade and crafts, the city was advanced in the arts of wood carving and jewelry. After the reunification of Russia and the Ukraine in 1654, Kaluga's role as a trade intermediary between Moscow and the Ukraine contributed also to its economic development. On August 24, 1776, Catherine the Great issued a decree establishing Kaluga Viceroyalty to unite Kaluga and Tula Governorates. The center of the viceroyalty acquired a new image. During the rule of Paul I, in 1795 Kaluga Viceroyalty was transformed into a governorate. During the Great Patriotic War, the territory was liberated from German occupation by the Soviet Army's 10th, 16th, 33rd, 43rd, 49th, 50th, and 61st Armies, the 20th Tank Brigade, 1st Air Army, 1st Cavalry Corps, and the Normandy squadron. The modern oblast was founded in accordance with the decree of the Presidium of the Supreme Soviet of the USSR of July 5, 1944. After the dissolution of the Soviet Union, Kaluga Oblast became a federal subject of the Russian Federation. In March 1996, the Charter of Kaluga Oblast was adopted. According to the results of the 2010 Census, the population of the oblast is 1,010,930; down from 1,041,641 recorded in the 2002 Census, and further down from 1,066,833 recorded in the 1989 Census.