Taking the city of Torzhok on 5 March 1238 after a two-week siege, the Mongols continued to Novgorod. However, they failed to reach the city, mainly because they had difficulties moving in the woods, and after advancing around 100 kilometers at the unknown place designated in the chronicles as the Ignach Cross, they abandoned the plans to conquer Novgorod, turned south, and divided into two groups. Some of the forces led by Kadan and Storms passed over the Eastern route through the Ryazan land. The main forces led by Batu Khan passed through Dolgomost 30 km east of Smolensk, then entered the Chernigov Principality on the upper Gums, burned Vshchizh, but then abruptly turned to the northeast, bypassing the Bryansk and Karachev, at the end of March 1238 went to the Kozelsk on the Zhizdra River.

At that time the city was the capital of the Principality at the head of twelve-year-old Prince Vasily, grandson of Mstislav Svyatoslavich of Chernigov, who was killed at the Battle of Kalka in 1223. The city was well fortified: surrounded by ramparts built on them walls, but the Mongols had powerful siege equipment.

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.