(Καΰστριος), a son of Achilles and the Amazon Penthesileia, from whom the river Caystrus was believed to have derived its name. Caystrius, together with Asius, had a heroum on the banks of that river. (Strab. xiv. p.650; Serv. ad Aen. 11.661.)
[L.S]A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890