Simois (Simoeis) is the river-god of the small Trojan stream that rose on Ida (Mount Cotylus) and joined the Scamander below Troy — today the Dümrek Çayı, no longer a Scamander tributary. Son of Oceanus and Tethys, he fathered Astyoche (wife of Erichthonius) and Hieromneme (wife of Assaracus). In Iliad 21 Scamander calls him to swell against Achilles, but Hephaestus's fire subdues Scamander before Simois can answer.
Adapted from Wikipedia, "Simois" · CC BY-SA 4.0
I.River and family
The Simoeis was a small river of the Troad with its source in Mount Ida — more precisely Mount Cotylus — passing Troy and joining the Scamander below the city. Homer speaks of it often as a rapid mountain torrent. Its modern course has shifted so that it flows into the Hellespont directly rather than into the Scamander.
Like other river-gods he is son of Oceanus and Tethys. Two daughters married into the Trojan royal house: Astyoche to Erichthonius, Hieromneme to Assaracus.
II.The Trojan War
When the gods took sides, Simois supported Troy. In Iliad 21 Scamander, hard-pressed by Achilles, calls him to fill his streams from their springs, stand in a great wave, and raise a roar of timbers and rocks against the hero. Before Simois can respond, Hephaestus saves Achilles by subduing Scamander with flame — the twin rivers of the plain checked together in the poem's river battle.
The atlas pairs him with scamander as the Trojan water-gods; he is not a mortal namesake.