Hyllus or Hyllos (Greek, Modern (1453-);: Ὕλλος) was the ancient name of a river of Asia Minor. It is a tributary of the river Hermus, in Lydia, flowing into Hermus from the north.[1] In the time of Strabo, the river was called Phrygius.[2] Today's Turkish name is Kum Çayı.[3]