The word "Parthia" is originally traced to an inscription recorded in 520 BCE by the Achaemenian King Darius I, who referred to "Parthava," a land corresponding approximately with Khorasan in modern Iran. Later the term would come to refer to an empire, the beginnings of which would be established in this same area in 247 BCE. The origins of the Parthian Empire are not clear to historians, though tradition tells us that the first emperor was named Arsaces I, a former governor under the Bactrian Greeks. It is believed that sometime in the last decades of the third century BCE, Arsaces took up arms against his Greek monarch and established his own kingdom of Parthia. Arsaces and his successors consolidated their control over lands south of the Caspian Sea, and through a number of military campaigns, began to build an empire.
By the end of the second century BCE, the Parthians controlled all of the Iranian Plateau, the Tigris-Euphrates river valley, and much of Syria. They established their first treaty in 92 BCE with their future rivals, the Romans, in an effort to defeat their common enemy, the Seleucids. As the Seleucids weakened, the Parthians absorbed much of their territory. By the middle of the first century BCE, the Parthian Empire was at its zenith, both stable and strong.
Aristocrats appointed as regents by the Parthian throne ruled the empire on the local level. In the first few centuries of their empire, this Parthian ruling class continued to observe many aspects of Hellenistic culture that had characterized the upper levels of society under the Greco-Bactrian kings. Greek inscriptions and Greek-style portraiture mark early Parthian coins, bearing witness to this "Hellenophilic" stage of the Parthian Empire. Later, the Parthian kings began to redefine themselves as the direct heirs of the Achaemenian Empire; Mithridates II (123-87 BCE) is believe to be the first Parthian ruler to use the old Achaemenian title "King of Kings" on his coins, rather than the corresponding Greek title. From this time on, Parthian culture developed as a synthesis of Greek and Achaemenian culture, with local Iranian patterns gradually supplanting Hellenistic elements.
The Parthians controlled the overland trade routes between Asia and the Mediterranean, a position that brought great financial prosperity. Parthian merchants became very wealthy as resellers of Central Asian and Chinese wares, particularly silk. Parthian crafts and products were also widely traded, with textiles and woven fabrics in particularly high demand.
It appears that various religions were practiced in Parthia with minimal conflict, though Zoroastrianism gained increasing importance over the centuries. Buddhism was practiced in the easternmost reaches of the Parthian Empire, and Parthian religious scholars are known to have undertaken missions to China in order to study with Han-era Buddhist teachers.1
Beginning in the first century BCE, the Romans and Parthians engaged in a series of indecisive wars that lasted for almost three hundred years. They fought primarily over Syria, Mesopotamia and Armenia, with the lands passing first to Roman hands, and then back to the Parthians in successive battles. Since this did more to deplete resources on both sides than to achieve any lasting results, the resulting stalemate gave way to almost a century of peace.
In 114 CE, Roman forces once again pushed into Parthia, and in the ensuing campaigns, Rome was able to permanently retake territories that had earlier passed back and forth between them and Parthia. The Parthians were able to avoid complete defeat and held onto much of the Iranian plateau, but the end of the second century saw a weakening of the central Parthian power base. By the time of the last war with Rome in 195, a number of regents had became wealthy and powerful enough to defy the central authority of the throne, and refused to supply taxes and soldiers. In 224, internal rebellion led by the king of Pars grew into civil war. The last Parthian king, Artabanus V, was killed in battle by Parsian king Ardashir I, who went on to reunite Iran under the new Sassanian Empire.
(1) G.A. Koshelenko and V.N. Pilipko, "Parthia," History of Civilizations of Central Asia, volume II (Paris: UNESCO Publishing, 1996), pp. 149-150.