2. Disturbances having arisen in the countries beyond the Taurus in consequence of the kings of Syria and Media, who possessed the tract of which we are speaking, being engaged in other affairs,[1010] those who were intrusted with the government of it occasioned first the revolt of Bactriana; then Euthydemus and his party the revolt of all the country near that province. Afterwards Arsaces, a Scythian, (with the Parni, called nomades, a tribe of the Dahæ, who live on the banks of the Ochus,) invaded Parthia, and made himself master of it. At first both Arsaces and his successors were weakened by maintaining wars with those who had been deprived of their territory. Afterwards they became so powerful, in consequence of their successful warfare, continually depriving their neighbours of portions of their territory, that at last they took possession of all the country within the Euphrates. They deprived Eucratidas, and then the Scythians, by force of arms, of a part of Bactriana. They now have an empire comprehending so large an extent of country, and so many nations, that it almost rivals that of the Romans in magnitude. This is to be attributed to their mode of life and manners, which have indeed much of the barbarous and Scythian character, but are very well adapted for establishing dominion, and for insuring success in war. 3. They say that the Dahæ Parni were an emigrant tribe from the Dahæ above the Mæotis, who are called Xandii and Parii. But it is not generally acknowledged that Dahæ are to be found among the Scythians above the Mæotis, yet from these Arsaces according to some was descended; according to others he was a Bactrian, and withdrawing himself from the increasing power of Diodotus, occasioned the revolt of Parthia. We have enlarged on the subject of the Parthian customs in the sixth book of historical commentaries, and in the second of those, which are a sequel to Polybius: we shall omit what we said, in order to avoid repetition; adding this only, that Poseidonius affirms that the council of the Parthians is composed of two classes, one of relatives, (of the royal family,) and another of wise men and magi, by both of which kings are chosen. CHAPTER X. 1. Aria and Margiana, which are the best districts in this portion of Asia, are partly composed of valleys enclosed by [CAS. 516] mountains, and partly of inhabited plains. Some tribes of Scenitæ (dwellers in tents) occupy the mountains; the plains are watered by the rivers Arius and by the Margus. Aria borders upon Bactriana, and the mountain[1011] which has Bactriana at its foot. It is distant from [the] Hyrcania[n sea] about 6000 stadia. Drangiana as far as Carmania furnished jointly with Aria payment of the tribute. The greater part of this country is situated at the foot of the southern side of the mountains; some tracts however approach the northern side opposite Aria.