M.) DEiOTARUS, a tetrarch of Galatia (Gallo-Graecia) in Asia Minor, and a faithful ally of the Romans.
On the outbreak of the civil war, DeIotarus naturally sided with his old patron Pompey, and after the battle of Pharsalus escaped with him to Asia.
In the meantime Pharnaces, the son of Mithradates, had seized Lesser Armenia, and defeated DeIotarus near Nicopolis.
In consequence of the complaints of certain Galatian princes, DeIotarus was deprived of part of his dominions, but allowed to retain the title of king.
On the death of Mithradates of Pergamum, tetrarch of the Trocmi, DeIotarus was a candidate for the vacancy.
Other tetrarchs also pressed their claims; and, further, DeIotarus was accused by his grandson Castor of having attempted to assassinate Caesar when the latter was his guest in Galatia.
Cicero, who entertained a high opinion of Deiotarus, whose acquaintance he had made when governor of Cilicia, undertook his defence, the case being heard in Caesar's own house at Rome.
In his speech Cicero briefly dismisses the charge of assassination, the main question being the distribution of the provinces, which was the real cause of the quarrels between DeIotarus and his relatives.
After Caesar's death, Mark Antony, for a large monetary consideration, publicly announced that, in accordance with instructions left by Caesar, DeIotarus was to resume possession of all the territory of which he had been deprived.
When civil war again broke out, DeIotarus was persuaded to support Brutus and Cassius, but after the battle of Philippi went over to the triumvirs.
Part of it was handed over by Pompey to client princes: the coast-land east of the Halys (except the territory of Amisus) and the hill-tribes of Paryadres were given, with Lesser Armenia, to the Galatian chief Deiotarus, with the title of king; Comana was left under the rule of its high-priest.
The Pontic possessions of Deiotarus (d.
But this arrangement soon gave way before the ambition of one of these tetrarchs, Deiotarus, the contemporary of Cicero and Caesar, who made himself master of the other two tetrarchies and was finally recognized by the Romans as king of Galatia.
Under Diocletian's reorganization Galatia was divided, about 295, into two parts and the name retained for the northern (now nearly identical with the Galatia of Deiotarus); and about 390 this province, amplified by the addition of a few towns in the west, was divided.
Claudius Marcellus (pro Marcello), to plead in the same year before Caesar for Quintus Ligarius, and in 45 on behalf of Deiotarus, tetrarch of Galatia, also before Caesar.