Sozh River
Failing to get along with his uncle, on 10 April 1077 Oleg fled to his brother Roman who reigned in Tmutarakan. Together with his cousin, Boris Vyacheslavich, who had also settled in Tmutarakan, Oleg made an alliance with the Cumans and invaded Rus' in the summer of 1078. They routed their uncle, Vsevolod on the Sozh River and entered Chernigov on 25 August. The "Russian Primary Chronicle" accuses Oleg and Boris of being the first to lead "the pagans to attack the land of Rus'". However, Vladimir Monomach, in his "Instruction", reveals that he and his father, Vsevolod had hired Cumans when attacking Polotsk in the previous year.