(Ἀριαῖος), or ARIDAE'US (Ἀριδαῖος), the friend and lieutenant of Cyrus, commanded the barbarians in that prince's army at the battle of Cunaxa, B. C. 401. (Xen. Anab. 1.8.5; Diod. 14.22; comp. Plut. Art. 100.11.) After the death of Cyrus, the Cyrean Greeks offered to place Ariaeus on the Persian throne; but he declined making the attempt, on the ground that there were many Persians superior to himself, who would never tolerate him as king. (Anab. 2.1.4, 2.1.) He exchanged oaths of fidelity, however with the Greeks, and, at the commencement of their retreat, marched in company with them; but soon afterwards he purchased his pardon from Artaxerxes by deserting them, and aiding (possibly through the help of his friend Menon) the treachery of Tissaphernes, whereby the principal Greek generals fell into the hands of the Persians. (Anab. 2.2.8, &c., 4. §§ 1, 2, 9, 5. §§ 28, 38, &c.; comp. Plut. Art. 100.18.) It was perhaps this same Ariaeus who was employed by Tithraustes to put Tissaphernes to death in accordance with the king's order, B. C. 396. (Polyaen. 8.16; Diod. 14.80; Wess. and Palm. ad loc. ; comp. Xen. Hell. 3.1.7.) In the ensuing year, B. C. 395, we again hear of Ariaeus as having revolted front Artaxerxes, and receiving Spithridates and the Paphlagonians after their desertion of the Spartan service. (Xen. Hell. 4.1.27; Plut. Ages. 100.11.)