Achaemenid Satrapies > Parthia
Parthia roughly corresponds to a region in northeastern Iran. It was bordered by the Karakum desert in the north, included Kopet Dag mountain range and the Dasht-e-Kavir desert in the south. It bordered Media on the west, Hyrcania on the north west, Margiana on the north east, and Aria on the south east. During Arsacid times, Parthia was united with Hyrcania as one administrative unit, and that region is therefore often (subject to context) considered a part of Parthia proper. As the region inhabited by Parthians, Parthia first appears as a political entity in Achaemenid lists of governorates ("satrapies") under their dominion. Prior to this, the people of the region seem to have been subjects of the Medes, and 7th century BC Assyrian texts mention a country named Partakka or Partukka (though this "need not have coincided topographically with the later Parthia").
A year after Cyrus the Great's defeat of the Median Astyages, Parthia became one of the first provinces to acknowledge Cyrus as their ruler, "and this allegiance secured Cyrus' eastern flanks and enabled him to conduct the first of his imperial campaigns – against Sardis." According to Greek sources, following the seizure of the Achaemenid throne by Darius I, the Parthians united with the Median king Phraortes to revolt against him. Hystaspes, the Achaemenid governor of the province (said to be father of Darius I), managed to suppress the revolt, which seems to have occurred around 522–521 BC.
The first indigenous Iranian mention of Parthia is in the Behistun inscription of Darius I, where Parthia is listed (in the typical Iranian clockwise order) among the governorates in the vicinity of Drangiana. The inscription dates to c. 520 BC. The center of the administration "may have been at [what would later be known as] Hecatompylus". The Parthians also appear in Herodotus' list of peoples subject to the Achaemenids; the historiographer treats the Parthians, Chorasmians, Sogdians and Areioi as peoples of a single satrapy (the 16th), whose annual tribute to the king he states to be only 300 talents of silver. This "has rightly caused disquiet to modern scholars."
At the Battle of Gaugamela in 331 BC between the forces of Darius III and those of Alexander the Great, one such Parthian unit was commanded by Phrataphernes, who was at the time Achaemenid governor of Parthia. Following the defeat of Darius III, Phrataphernes surrendered his governorate to Alexander when the Macedonian arrived there in the summer of 330 BC. Phrataphernes was reappointed governor by Alexander.