Of the first writers who take the subject into their consideration, some are content to say that the Parthians were a race of Scyths, who at a remote date had separated from the rest of the nation, and had occupied the southern portion of the Chorasmian desert, whence they had gradually made themselves masters of the mountain region adjoining it.

Others added to this that the Scythic tribe to which they belonged was called the Dahse; that their own proper name was Parni, or Aparni; and that they had migrated originally from the country to the north of the Palus Maeotis, where they had left the great mass of their fellow tribesmen.

Subsequently, in the time of the Antonines, the theory was started that the Parthians were Scyths, whom Sesostris, on his return from his Scythian expedition, brought into Asia and settled in the mountain-tract lying east of the Caspian.
It can scarcely be thought that these notices have very much historical value.

Moderns are generally agreed that the Scythian conquests of Sesostris are an invention of the Egyptian priests, which they palmed on Herodotus and Diodorus.

Could they be regarded as having really taken place, still the march back from Scythia to Egypt round the north and east of the Caspian Sea would be in the highest degree improbable.