The Battle of the Sit River begins two centuries of Mongol horde domination of Rus.

The Battle of the Sit River took place on 4 March 1238 between the Mongol hordes of Batu Khan and the Suzdalians under Grand Prince Yuri II of Vladimir-Suzdal during the Mongol invasion of Kievan Rus'. It was fought in the northern part of the present-day Sonkovsky District of Tver Oblast of Russia, close to the selo of Bozhonka.

An orda or horde was a historical sociopolitical and military structure found on the Eurasian Steppe, usually associated with the Turkic and Mongol peoples. This form of entity can be seen as the regional equivalent of a clan or a tribe of nomads. Some successful ordas gave rise to khanates. The original term did not carry the meaning of a large khanate such as the Golden Horde. These structures were contemporarily referred to as ulus.