After this defeat, Antiochus began an expedition into Iran, but was killed in Elymaïs.[3] The Arsacids then took power in Parthia and declared their full independence from the Seleucid Empire. In 148 BC, the Parthian king Mithridates I invaded Media which was already in revolt against the Seleucid empire, and in 141 BC the Parthians captured the major Seleucid city of Seleucia (which was the eastern capital of the Seleucid empire).[4] These victories gave Mithridates control over Mesopotamia and Babylonia. In 139 BC the Parthians defeated a major Seleucid counterattack, breaking the Seleucid army, and captured the Seleucid King, Demetrius II, thus effectively ending Seleucid claims to any land east of the Euphrates river.