Иоанн Скилица
The annihilation of Khazaria was undertaken against the background of the Rus'-Byzantine alliance, concluded in the wake of Igor's Byzantine campaign in 944. Close military ties between the Rus' and Byzantium are illustrated by the fact, reported by John Skylitzes, that a Rus' detachment accompanied Byzantine Emperor Nikephoros Phokas in his victorious naval expedition to Crete.