The rise of the Parthians in Iran
Invasion of the Parni
Arsaces, who was leading Parni (a member tribe of the Dahae confederation), must have commenced his struggle against the Seleucids from 247 BC, the year from which the Parthians dated their history. This does not essentially mean that Arsaces was crowned king in 247. Other Iranian dynasties (for example, the Sāsānids) dated the beginning of their epochs from the time when they started to establish their influence rather than from the time of coronation of the first monarch of their line.
Daho-Parno-Parthian tribes “selected princes for peace and chiefs for war” from amongst the closest circle of the royal household. They were well-known for their breeding of horses, their fine archers and their combat cavalry. Alexander bumped into them during his Bactrian campaign, and the Greek writers who recorded his reign commented on their effectiveness and agility as horsemen. They were a people who preserved the traditions of patriarchal tribal organization. The Parni, with Arsaces in the lead, captured the province of Parthia after having defeated Andragoras; soon Hyrcania in the neighbourhood was annexed, and the Parni reached the Caspian Sea. Arsaces got himself crowned in the city of Asaak, and the tribe named itself the Parthians. Their language was closely linked to Scythian and Median. The dynasty these people created never broke it’s connect with the people, and rare was the Arsacid dynastic sovereign who did not turn to his people when in danger.
Formation of the Parthian state
Even though the two new kingdoms, that of Arsaces I’s Parthians and the Greco-Bactrian kingdom of Diodotus I, sprang up almost at the same time and quite close to each other, there were some prominent differences between them. The force that was behind the rebellion in Bactria was a relationship—or maybe even an association—between the local nobility (large landholders who controlled the whole indigenous population) and the local Greek community. Both groups were not happy with the Macedonian domination embodied by the Seleucid dynasty.
The makeup of the Parthian kingdom appears to have been quite unique. It was basically built on the relationship of the people of Parthia to the neighbouring tribes outside the static borders—an ethnic mass, half settled and half nomadic, that inhabited the north of Iran. The triumph of Arsaces and his men was based on their spirit, their strength, and the weakness of their enemies. The Greek element existing in Parthia does not seem to have played a part similar to that played by its counterpart in Bactria. Actually, the Parthians, at least at the outset, may have been hostile to the local Greek populations. During their war with Antiochus III, they massacred all the Greek people of the city of Syrinx in Hyrcania.