The leader of the Parni, one of the three tribes of the Dahae confederacy, Arsaces founded his dynasty in the mid-3rd century BC when he conquered the satrapy of Parthia (now shared between Turkmenistan and Iran) from Andragoras, who had rebelled against the Seleucid Empire.

[5] According to Roman historian Ammianus Marcellinus, Arsaces was a bandit of low birth, who invaded and conquered Parthia, killing its satrap Andragoras, who had recently declared independence from the Hellenistic Seleucid Empire.

[6] The most accepted theory is the one by the Greek geographer Strabo:[7][5][8] according to him, Arsaces was a Scythian or a Bactrian chieftain, who became the leader of the Parni, one of the three tribes of the Dahae confederacy of Central Asia.

[9] The Dahae relied their strength completely on horseback, and thus possessed an extremely mobile force, which was able to retreat to the south of the Aral Sea when endangered.

[11] They gradually started settling in Parthia, a region in the south-eastern part of the Caspian Sea, that almost corresponded to present-day Khorasan Province of Iran and southern Turkmenistan.

[19] According to the French historian Jérôme Gaslain, Arsaces could have arguably spent much of his life in the Seleucid lands, and may even have belonged to the local elite of Parthia.

[22] Following the secession of Parthia from the Seleucid Empire and the resultant loss of Seleucid military support, Andragoras had difficulty in maintaining his borders, and about 238 BC—under the command of Arsaces and his brother Tiridates I[8][23] the Parni invaded Parthia and seized control of Astabene (Astawa) from Andragoras, the northern region of that territory, the administrative capital of which was Kuchan.

[7] Indeed, Arsaces' withdrawal to the Apasiacae was perhaps a strategic move, since Seleucus II neither possessed the resources to chase him nor the time to conclude a peace treaty.

The now-deprecated narrative of the foundation of the Arsacid dynasty by Arsaces and his brother Tiridates, who led the Parni in revolt together, was established by Jean Foy-Vaillant in 1725.

[32][33] This led to some different theories, including one that considered Arsaces a legendary figure, whilst attributing the foundation of the Arsacids to Tiridates.

[34] Between 1957 and 1962 Józef Wolski [pl] published a series of articles with the opposite view: he regarded Arsaces as the founder of the Arsacids, and Tiridates as legendary.

[37] Khodadad Rezakhani adds that his coins took many stylistic elements from Seleucids and earlier Achaemenid satrapal issues, but he nonetheless made several innovations that differentiated them from those of his predecessors.

[38] According to Alireza Shapour Shahbazi, on his coins, Arsaces "deliberately diverges from Seleucid coins to emphasize his nationalistic and royal aspirations";[5] the typical Seleucid figure of Apollo seated on the omphalos and holding a bow is replaced by an archer imitating Arsaces,[b] who is seated on a stool (done in the same fashion as some Achaemenid satraps, such as Datames) whilst wearing Sakaian clothing and a soft cap, known as the bashlyk.

[5] Some of the inscriptions on Arsaces' coins calls him kārny[c] (the Greek equivalent being autokrator), which was a title carried by prominent Achaemenid military leaders, such as Cyrus the Younger.

[39] For instance, Arsaces wears the pointed soft cap on the obverse, similar to coins of the Achaemenid era, as does the archer on the reverse who is dressed in an Iranian riding costume.

[30][51][e] The name also connected the Arsacids with the legendary Kayanian ruler Kavi Arshan, whose dynasty must still have been remembered by the inhabitants of eastern Iran, such as the Parthians and the Dahae.