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The English-Latin noun vates // is a term for a prophet, following the Latin term. It is the origin of the English term ovate for an Irish bard. The earliest Latin writers used vātēs ([ˈwaːteːs] to denote "prophets" and soothsayers in general; the word fell into disuse in Latin until it was revived by Virgil. Thus Ovid could describe himself as the vates of Eros (Amores 3.9).
According to the Ancient Greek writers Strabo, Diodorus Siculus, and Poseidonius, the vates (οὐάτεις) were one of three classes of Celtic priesthood, the other two being the druids and the bards. The Vates had the role of seers and performed sacrifices (in particular administering human sacrifice) under the presidence of a druid according to Roman and Christian interpretation. Their role therefore corresponded to that of an Adhvaryu in Vedic religion. The Celtic word vates is continued by Irish fáith "prophet, seer," and gwawd "scorn, satire, scoff" in Welsh.
It is unknown whether the Latin and Gaulish usages are cognates, or if the former should be considered a Celtic loanword. The word may be derived from a PIE root *wāt- " to inspire, spiritually arouse"; however that root cannot be shown to go back to Proto-Indo-European, since it is only certainly attested for Celtic and Germanic (though it may be present natively in Italic). Virgil uses the Latin vannus "winnowing fan" (from *wat-nos, compare Old High German wadal, modern German Wedel, with the same meaning, from *wat-lo-) for something borne about in the Bacchic festival, suggesting that the root may have had an ecstatic sense in Italic also.
In pagan Rome the vates resided on the Vatican Hill, the Hill of the Vatii. Indeed, the Vatican Hill takes it name from the Latin word Vaticanus, a vaticiniis ferendis, in allusion to the oracles, or Vaticinia, which were anciently delivered on the Vatican Hill.
Modern usage 
An ovate is also the initial level one can attain in the modern Welsh Gorsedd of Bards. The Gorsedd is not a neo-druidic entity like the one mentioned above, but is more concerned with Welsh arts and culture; however, the ceremony and practices are largely based on reimaginings of druidism by Iolo Morganwg.
- Ovates or Vates: The Shamans
- Sources: Compendious Description of the Museums of Ancient Sculpture, Greek and Roman, in the Vatican Palace, by Cav. H. J. Massi, First Curator of the Vatican Museums and Galleries, Paleographer and Professor of the Italian and French Languages, Rome, Third Edition, 1889, Title page, page 7.
- Perkins, Caroline A., "Ovid's Erotic Vates" in Helios, March 2000
- Rübekeil, Ludwig, Wodan und andere forschungsgeschichtliche Leichen: exhumiert, Beiträge zur Namenforschung (2003), 25–42.
- Peter Berresford Ellis, "The Druids", William B. Eerdmans Publishing (1995) ISBN 0-828-3798-0