B. xi. c. ix. 3. PARTHIA. ARIA. MARGIANA. 251 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 Dahse, 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 de- prived of their territory. Afterwards they became so powerful, in consequence of their successful warfare, continually depriv- ing 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 cha- racter, but are very well adapted for establishing dominion, and for insuring success in war. 3. They say that the Dahae Parni were an emigrant tribe from the Dahas above the Ma3otis, who are called Xandii and Parii. But it is not generally acknowledged that Dahse are to be found among the Scythians above the Ma3otis, yet from these Arsaces according to some was descended ; ac- cording to others he was a Bactrian, and withdrawing him- self 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 com- posed 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. ARTA and Margiana, which are the best districts in this portion of Asia, are partly composed of valleys enclosed by