The Parni (//; Ancient Greek: Πάρνοι, Parnoi) or Aparni (//; Ἄπαρνοι, Aparnoi) were an east Iranian people of the Ochus (Ancient Greek: Ὧχος Okhos) (Tejen) River valley, southeast of the Caspian Sea. The Parni were one of the three tribes of the Dahae confederacy.
There is no unambiguous evidence of the Parnian in native Iranian language sources,cf.  and all references to these people comes from Greek and Latin accounts. In these accounts, which are not necessarily contemporaneous, it is difficult to unambiguously identify references to the Parni due to inconsistency of Greek/Latin naming and transliteration, and/or the similarity to names of other tribes such as the 'Sparni' or 'Apartani' and the 'Eparnoi' or 'Asparioi'. It may also be that the Parni are related to one or more of these other tribes, and that "their original homeland may have been southern Russia from where they emigrated with other Scythian tribes." The present-day localization of the Dahae Parni is formed by Strabo's (Geographica 11, 1st century BCE) identification of the Parni/Dahae in the region of the Caspian Sea. This roughly corresponds to historic 'Sakastan', which gets its name from the Sakas/Scythians.
While 'Dahae' is preserved in 'Dahestan'/'Dihistan', a district "on the eastern shore of the Caspian Sea," "an urban center of the ancient Dahae (if indeed they possessed one) is quite unknown." 
The language[c] of the Parni is not directly attested but is assumed to be one of the eastern substrates of the subsequently recorded Parthian language, which the Parni eventually adopted. To the "incoming Parni may be ascribed a form of speech showing a strong east Iranian element, resulting from their proximity on the steppe to east Iranian Sakas." Through the influence of the Parthians in Armenia, traces of the Parni language survive as "loan-words in Armenian."
The language of the Parni "was described by Justin as 'midway between Scythian and Median [and] contained features of both'" (41.1.10). Justin's late (3rd century) opinion is "no doubt slightly exaggerated," and is in any case of questionable veracity given the ambiguity of names.
Rise to prominence
In 247 BCE, Andragoras, the Seleucid governor (satrap) of Parthia ("roughly western Khurasan") proclaimed independence from the Seleucids, when - following the death of Antiochus II - Ptolemy III seized control of the Seleucid capital at Antioch, and "so left the future of the Seleucid dynasty for a moment in question."
Meanwhile, "a man called Arsaces, of Scythian or Bactrian[a] origin, [was] elected leader of the Parni tribes." 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 BCE - under the command of "Arsaces and his brother Tiridates" - the Parni invaded Parthia and seized control of Astabene (Astawa), the northern region of that territory, the administrative capital of which was Kabuchan (Kuchan in the vulgate).
A short while later, the Parni seized the rest of Parthia from Andragoras, killing him in the process. Although an initial punitive expedition by the Seleucids under Seleucus II was not successful, the Seleucids under Antiochus III recaptured Arsacid controlled territory in 209 BCE from Arsaces' (or Tiridates'[b]) successor, Arsaces II. Arsaces II sued for peace and accepted vassal status, and it was not until Arsaces II's grandson (or grand-nephew) Phraates I, that the Arsacids/Parni would again begin to assert their independence.
For the historiographers upon whose documentation the reconstruction of early Arsacid history depends, the Parni had by then become indistinguishable from the Parthians.
The seizure of Astabene in 238 BCE nominally marks the beginning of the Arsacid era, which is named after Arsaces, and the name adopted by all Parthian kings. "Arsaces" is a variant of (also Greek) "Artaxerxes," and the Arsacid dynasts laid claim to descend from Artaxerxes II. Beginning from Astabene and Parthia (which would subsequently be extended southwards to include much of present-day Sistan), the Arsacids gradually subjugated many of the neighboring kingdoms, most of which were thereafter controlled as vassalries. Beginning with the successful revolt - in 224 CE - of an erstwhile vassal of Stakhr named Ardashir (in Greek again "Arsaces"/"Artaxerxes"), the Arsacid/Parthian hegemony began to yield to a Sassanid/Persian one.
The name "Parni" reappears in Sassanid-era documents to identify one of the seven Parthian feudal families allied with the Sassanid court. However, this family is not attested from Arsacid times, and the claim to the "Parni" name is (like four of the six other families) "in all probability not in accordance with reality." "It may be that [...] members of them made up their own genealogies in order to emphasize the antiquity of their families."
It has been suggested that the Parnau Hills (Paran Koh) bear the name of the Parni.
- a^ Arsaces was "perhaps originally a local ruler in Bactria."
- b^ The origins of the Arsacids lineage are based on legend and what the later Greeks and Romans could make of these. While the tale of the two brothers may even be fiction (Wolski, 1937/1938), in general it is assumed that they were historical personae and that Tiridates (I) succeeded his brother Arsaces (I), but took on the Arsaces name at his coronation. Adding to the confusion is the relationship between Tiridates I (a.k.a. Arsaces II) and his son and successor Arsaces II (a.k.a. Artabanus I). See also Bivar's rejection of the genealogies proposed by Frye and Chaumont & Bickermann.
- c^ In linguistics and philology, the expression 'Parnian' is sometimes used as a term of convenience to collectively denote eastern Iranian influences evident in the (western Iranian) Paenur language. Because the language of the Parni is not actually attested, it is not possible to determine whether there is actually a specific correlation between the language of the Parni and that of the east Iranian element in Parthian.
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- Lendering, Jona (2006), The Parni, Amsterdam: livius.org
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- Rawlinson, Henry C. (1879), "The Road to Merv", Proceedings of the Royal Geographical Society and Monthly Record of Geography, New Monthly Series 1 (3): 161–191, doi:10.2307/1800653
- Yarshater, Ehsan (2006), "Iran ii. Iranian History: An Overview", Encyclopaedia Iranica 13, New York: Encyclopaedia Iranica