Abbassus or Ambasum (Latin: Abbassus;^[1] Ἄμβασον^[2]), was an ancient town of Phrygia, on the frontiers of the Tolistoboii, in Galatia.^[3] It is, perhaps, the same as the Alamassus reported by of Hierocles,^[4] and the Amadasse whose bishops attended early church councils. The editors of the Barrington Atlas of the Greek and Roman World note that its probable location is near Synnada,^[5] however its precise location is not known.

 This article incorporates text from a publication now in the public domain: Smith, William, ed. (1854–1857). "Abbassus". Dictionary of Greek and Roman Geography. London: John Murray.