The battles during the Siege of Dorostolon were fought in 971 between the Byzantine Empire and forces of Kyiv Rus. Byzantine court historian and chronicler Leo the Deacon provided his eyewitness description of the sacrifice: “When night fell, since the moon was nearly full, they [the Rus] came out on the plain and searched for their dead; and they collected them in front of the city wall and kindled numerous fires and burned them, after slaughtering on top of them many captives, both men and women, in accordance with their ancestral custom. And they made sacrificial offerings by drowning suckling infants and chickens in the Istros [Danube], plunging them into the rushing waters of the river. For they are said to be addicted to Hellenic mysteries, and to make sacrifices and libations to the dead in the Hellenic fashion, having been initiated in these things either by their own philosophers, Anacharsis and Zamolxis, or by the comrades of Achilles. For Arrian says in the Periplous that Achilles, son of Peleus, was a Scythian, from a small town called Myrmekion located by Lake Maeotis; and that he was banished by the Scythians because of his harsh, cruel, and arrogant temperament, and then went to live in Thessaly.”
The “Gardariki, Ukraine” e-book has all the facts about that campaign and several more burial rituals in the times of Kyiv Rus that can be qualified as the Scythian ones.