The Aros River was a river that ran through Beleriand in Middle-earth during the First Age. The Aros River was a tributary of the river Sirion. The Aros River runs on and it rises in the northern lands around Himring. Then it meets the Siron at Aelin-uial. The Aros River formed the eastern and southern borders of the Kingdom of Doriath and joined the Sirion at the Kingdom's southwest corner.