Nothing is known of the history of this city, which Ptolemy locates in Great Phrygia, and 6th-century Hierocles, in Phrygia Pacatiana, whose capital was Laodicea. It has a few inscriptions but no ruins.
The 2013 edition of the Annuario Pontificio puts Synaus in the late Roman province of Phrygia Pacatiana Secumda whose civil capital and metropolitan see was Hierapolis. In the early 20th century, Sophrone Pétridès placed it in Phrygia Pacatiana Prima, whose capital and metropolitan see was Laodicea on the Lycus.
According to Pétridès, in 1394 the see of Synaus was united to that of Philadelphia (Roman province of Lydia); in the 7th century it was a suffragan of Laodicea on the Lycus (in Phrygia Pacatiana Prima); it seems also that at this time it was united to the see of Ancyra Ferrea (in Phrygia Pacatiana Secunda). In the 9th century it was attached to the metropolis of Hierapolis (capital of Phrygia Pacatiana Secunda) and remained so till its disappearance, as appears from the Greek Notitiae episcopatuum.
To these may be added Stephanus, whose name occurs in the inscription (8th century?) "Corp. inser. græc.", 8666 perhaps the Stephanus mentioned in 787.