Слово о полку Игореве
In 1096, Oleg I of Chernigov (also referred to as "Oleh") created a large Severian Principality, which stretched as far as the upper reaches of the Oka River. Until the end of the century, the principality served as a buffer state against Cuman attacks. Its most celebrated ruler was Prince Igor (1150–1202), whose exploits are recounted in the 12th century epic "The Tale of Igor's Campaign".