CAYSTER, or CAYSTRUS, (anc. geog.), a river of Ionia, whose mouth Ptolemy places between Colophon and Ephesus; commended by the poets for its swans, which it had in great numbers. Its source was in the Montes Cilibiani, (Pliny). Caystrus Campus was a part of the territory of Ephesus. Campi Caystriani of Lydia, were plains lying in the middle between the inland parts and mount Tmolus.