The Nymphaeum of Kestros (or Caystros), consecrated to the Lydian namesake river-god, is a monumental fountain that lies at the colonnaded end of the main street in the ancient city of Perga (Parha in Hittite) in southeast Anatolia (Minor Asia).
It was fashioned during the reign of Roman emperor Hadrian (second century AD) when the city had come under Roman rule.
The name Kestros apparently comes out of the Hittite Kastaraya for the river as it appears in a treaty between the Hittite King Tudḫaliya IV and his vassal king of Tarḫuntašša in the second half of the 13th century BC.