Mongol invasion of Rus'
The Siege of Kozelsk was one of the main events of the Western (Kipchak) March of the Mongols (1236–1242) and the Mongol invasion of Rus' (1237–1240) at the end of the Mongol campaign in North-Eastern Russia (1237–1238). The Mongols laid a siege in the spring of 1238 and eventually conquered and destroyed the town of Kozelsk, one of the subsidiary princely centers of the Principality of Chernigov.