Parthia, anciently a district in what is now northern Persia, lay between Media on the west and Bactria on the east, was separated from the Caspian Sea on the north by the savage land of Hyrcania, and was bordered on the south by the Iranian deserts. The Parthians were of Scythian descent, immigrants and nomads, who eventually adopted the Median dress and a semi-Aryan speech. But in war they clung to their national habits: they always fought on horseback, and both horse and rider were clad throughout in scale armour; their weapons were bows and arrows, which they discharged backwards during pretended flight as well as forwards in direct attack. Their armies were made up principally of slaves, commanded by their masters, the aristocratic nucleus of the Parthian nation. Parthia was subject successively to the Assyrians, the Medes, Persians, Greeks (Alexander the Great and his generals), and the Seleucids of Syria. In or about 250 B.C. a chief named Arsaces founded an independent kingdom in Hyrcania; his brother and successor, Tiridates, established himself in Parthia in 241 B.C. But the early kings of Parthia had much ado to maintain their position against their suzerains, the Seleucid 'great kings;' and it was not until Mithridates I. (171-138) ascended the throne, and had subdued Bactria, Media, and Babylonia, that the Parthian princes shook off completely the Syrian (Greek) yoke and became independent. This king made Parthia supreme in Iran. He greatly strengthened his power by resting it in great part upon the Magi (q.v.) and the ancient creed of Zoroaster. In the reign of his successor the Seleucid king made a determined effort to recover the lost provinces in Iran, but the expedition cost him his life and his army (129 B.C.). No sooner was this enemy disposed of than another and more formidable foe appeared in the east—the Scythians. They defeated and slew (128) Phraates, king of Parthia, levied tribute from his kingdom, and established themselves within its borders. During the first half of the 1st century the Parthian kings, by interfering in the affairs of Armenia, first came into contact with the Romans. The unprovoked invasion of Mesopotamia by Crassus (53 B.C.), his disastrous defeat and his death, make the first act in the drama of real contest that then ensued between Rome and Parthia. The remaining acts were the conquest of Syria and Palestine by Parthia (40-38); the disastrous campaign of Antony in Armenia (36 B.C.); then, after a century and a half of, in Parthia, mostly internal dissensions, the renewal of hostilities by Trajan (115-117 A.D.); the brilliant campaign of Avidius Cassius (164-165); the capture of Ctesiphon by Severus (199) and his repulse before Atrata (201); and the defeat of Macrinus, the Roman emperor, and his ignominious payment of fifty million denarii to his enemy (217-218). During nearly all this period the Euphrates was looked upon by both combatants as the frontier line between their respective empires. The Parthian capital was Ctesiphon, a suburb or twin-capital with Seleucia, all through the duel with Rome. The Parthian empire was overthrown in a battle fought in 224 (or 227) by Ardashir, a prince of Persis, a province of ancient Iran, who founded the subsequent dynasty of the Sassanids (see PERSIA). The Parthian kings during the most flourishing period of their power used Greek as their official language, adopted some of the Greek deities, and in other ways put themselves under the influence of Greek civilisation. But the hold of this civilisation grew weaker as time went on, and Greek ceased to be the official language in the 2d century A.D.
See histories of Parthia by Rawlinson (1873), Schneidewirth (Heiligenstadt, 1874), and Spiegel (Leip. 1887).