During his reign, Parthia was transformed from a small kingdom into a major political power in the Ancient East as a result of his conquests.

[7] The role of Mithra peaked under the Parthians, which according to the modern historian Marek Jan Olbrycht, "seems to have been due to Zoroastrian struggles against the spread of foreign faiths in the Hellenistic period.

[8] The kingdom that Mithridates inherited in 165 BC was one of the many medium-sized powers that had risen with the decline of Seleucid Empire or had appeared on its borders.

[9] He first turned his sights on the Greco-Bactrian Kingdom which had been considerably weakened as a result of its wars against the neighbouring Sogdians, Drangianans and Indians.

[8] The new Greco-Bactrian king Eucratides I (r. 171–145 BC) had usurped the throne and was as a result met with opposition, such as the rebellion by the Arians, which was possibly supported by Mithridates I, as it would serve to his advantage.

[20] Mithridates I shortly afterwards retired to Hyrcania, whilst his forces subdued the kingdoms of Elymais and Characene and occupied Susa.

[21] Whereas Hecatompylos had served as the first Parthian capital, Mithridates I established royal residences at Seleucia, Ecbatana, Ctesiphon and his newly founded city, Mithradatkert (Nisa), where the tombs of the Arsacid kings were built and maintained.

[24] The Seleucids were unable to retaliate immediately as general Diodotus Tryphon led a rebellion at the capital Antioch in 142 BC.

[34] Since the early 2nd century BC, the Arsacids had begun adding obvious signals in their dynastic ideology, which emphasized their association with the heritage of the ancient Achaemenid Empire.

[35][24] The Arsacid monarchs preceding Mithridates I are depicted on the obverse of their coins with a soft cap, known as the bashlyk, which had also been worn by Achaemenid satraps.

[42] In the Parthian era, Iranians used Hellenistic iconography to portray their divine figures, thus Heracles was seen as a representation of the Avestan Verethragna.

[46] Renamed Mithradatkert ("Mithridates' fortress"), the city was made into a religious hub that was dedicated to promote the worship of Arsacid family.

[46] A sculpted head broken off from a larger statue from Mithradatkert, depicting a bearded man with noticeably Iranian facial characteristics, may be a portrait of Mithridates I.

[48] According to Strabo, the city was established as a camp for the Parthian troops, due to Arsacids not finding it suitable to send them into Seleucia.

[51][52] The modern historian Trudy S. Kawami has suggested the figure might be Kamnaskires II Nikephoros, the second ruler of Elymais, who declared independence from the Seleucids.

[53] Of all Mithridates' accomplishments, his greatest one was to transform Parthia from a small kingdom into a major political power in the Ancient East.

[24] His conquests in the west seem to have been based on a plan to reach Syria and, thereby, gain Parthian access to the Mediterranean Sea.

[24] The modern historian Klaus Schippmann emphasises this, stating "Certainly, the exploits of Mithridates I can no longer simply be classified as a series of raids for the purpose of pillaging and capturing booty.