(Ἀρκαθίας), a son of Mithridates, joined Neoptolemus and Archelaus, the generals of his father, with 10,000 horse, which he brought from the lesser Armenia, at the commencement of the war with the Romans, B. C. 88. He took an active part in the great battle fought near the river Amneius or Amnias (see Strab. xii. p.562) in Paphlagonia, in which Nicomedes, the king of Bithynia, was defeated. Two years afterwards, B. C. 86, he invaded Macedonia with a separate army, and completely conquered the country. He then proceeded to march against Sulla, but died on the way at Tidaeum (Potidaea?) (Appian, App. Mith. 17, 18, 35, 41.)