BORYSTHENES was a river-god of Skythia (Scythia) in north-eastern Europe (modern Ukraine).
The Borysthenes River (now the Dneiper) flowed south across the steppe into the Black Sea. The most important neighbouring rivers were the Istros (Ister) (the Danube) in the west, and Tanais (the Don) in the east.
THOAS (Antoninus Liberalis 27)
CLASSICAL LITERATURE QUOTES
Antoninus Liberalis, Metamorphoses 27 (trans. Celoria) (Greek mythographer C2nd A.D.) :
"Iphigeneia she [the goddess Artemis] carried off far away from Greece, to the Sea of Pontos [i.e. the Black Seea] with its welcoming name of Euxinos, to Thoas son of [the river] Borysthenes. She called the tribe of nomads there Taurians because a bull (tauros) had appeared instead of Iphigeneia on the altar."
- Antoninus Liberalis, Metamorphoses - Greek Mythography C2nd A.D.