In 209 B.C., with one hundred thousand foot and twenty thousand horse, he marched against the new Parthian king, Arsaces II, son and successor of Tiridates. The war ended in a treaty which left Arsaces his kingdom, but beyond question reduced him to a vassal. In 208 B.C. began the much more serious war with Bactria. At length, in 206 B.C., a peace was arranged, and Antiochus was visited in his camp by Demetrius, the youthful son of Euthydemus, who pleased the king so well that he betrothed to him his daughter; Euthydemus was left on his throne, and the two powers swore an alliance offensive and defensive, which cost Bactria no more than certain payments of money, the victualling of the Macedonian troops, and the surrender of the war-elephants. The Bactrian Greeks were grateful for this moderation; their memorial coins place Antiochus Nicator with Euthydemus Theos, Diodotus Soter, and Alexander Philippi among the founders of their political existence. The kings of Parthia had long remained quiet after the war with Antiochus the Great. Priapatius, successor of Arsaces II (191-176 B.C.), calls himself on his coins “Arsaces Philadelphus,” perhaps because he had married a sister, and was the first of all Parthian kings to call himself “Philhellen.” By the last title he presents himself, at a time when the Seleucid power was sinking, as the protector of his present and future Greek subjects. His eldest son and successor, Phraates I (Arsaces Theopater of the coins), conquered the brave Mardian highlanders and transplanted them to Charax in the neighbourhood of the Caspian Gates, a proof that the Parthians had already detached Comisene and Choarene from Media, probably just after the death of Antiochus the Great. CONQUESTS OF MITHRIDATES About 171 B.C. Phraates died and left the crown not to his sons but to his brother Mithridates, a prince of remarkable capacity, who made Parthia the ruling power in Iran. His first conquests, it would seem, were made at the expense of Bactria.