Simoeis is a river of the Trojan plain and the name of its god. Like other river-gods, Simoeis is the son of Oceanus and Tethys.

Simoeis had two daughters who were married into the Trojan royal family. One daughter, Astyoche, was married to Erichthonius, and the other daughter, Hieromneme was the wife of Assaracus. When the gods took sides in the Trojan War, Simoesis supported the Trojans.

Scamander, another Oceanid who also supported the Trojans, called upon Simoeis for help in his battle against Achilles:

Illiad, 21:

But Scamander did not hold his fury back,
growing even more enraged at Peleus' son.
He raised himself up in a high-crested wave 
and called out with a shout to Simoeis:

                                                    "Dear brother,
let's both together counter this man's power,
since he'll soon demolish Priam's city.
Trojans will not stand up to him and fight. 
Come quickly. Help me.  Fill your streams
with water from your springs.  Whip up your torrents.
Then stand in a huge wave, raising a din
with rocks and tree trunks, so we can stop
this violent man, now in a conquering rage,    
like some god.

Before Simoeis can respond, Hephaestus was able to save Achilles by subduing Scamander with flame.

Reference

• March, J., Cassell's Dictionary Of Classical Mythology, London, 1999. ISBN 030435161X