Parthia (pär´thēə), ancient country of Asia, SE of the Caspian Sea. In its narrowest limits it consisted of a mountainous region intersected with fertile valleys, lying S of Hyrcania and corresponding roughly to the modern Iranian province of Khorasan. It was included in the Assyrian and Persian empires, the Macedonian empire of Alexander the Great, and the Syrian empire. The Parthians were famous horsemen and archers and may have been of Scythian stock.
In 250 BC, led by Arsaces, they freed themselves from the rule of the Seleucids and founded the Parthian empire. At its height, in the 1st cent. BC, this empire extended from the Euphrates across Afghanistan to the Indus and from the Oxus (Amu Darya) to the Indian Ocean. Defeating Marcus Licinius Crassus in 53 BC, the Parthians threatened Syria and Asia Minor, but they were turned back by Ventidius in 39–38 BC
Under Trajan the Romans advanced (AD 114–16) as far as the Persian Gulf, but they withdrew in the reign of Hadrian and were never again so successful against the Parthians. Then began the decline of the empire, which in AD 226 was conquered by Ardashir I (Artaxerxes), the founder of the Persian dynasty of the Sassanids. The chief Parthian cities were Ecbatana, Seleucia, Ctesiphon, and Hecatompylos. Such expressions as "a Parthian shot" were suggested by the Parthian ruse in which mounted men used their arrows effectively while in simulated flight.
See N. C. Debevoise, A Political History of Parthia (1938, repr. 1970); P. B. Lozinski, The Original Homeland of the Parthians (1959); M. A. R. Colledge, The Parthians (1967).