The reign of Mithridates I. is the most important in the Parthian history. [PLATE 1. Fig. 3.] Receiving from his brother Phraates a kingdom of but narrow dimensions, confined (as it would seem) between the city of Charax on the one side, and the river Arius, or Hori-rud, on the other, he transformed it, within the space of thirty-seven years (which was the time that his reign lasted), into a great and nourishing Empire. It is not too much to say that, but for him, Parthia might have remained a more petty State on the outskirts of the Syrian kingdom, and, instead of becoming a rival to Rome, might have sunk shortly into obscurity and insignificance. [Illustration: PLATE 1.] As commonly happens in the grand changes which constitute the turning-points of history, the way for Mithridates’s vast successes was prepared by a long train of antecedent circumstances. To show how the rise of the Parthians to greatness in the middle of the second century before our era was rendered possible, we must turn aside once more from our proper subject and cast a glance at the condition of the two kingdoms between which Parthia stood, at the time when Mithridates ascended the throne. The Bactrian monarchs in their ambitious struggles to possess themselves of the tracts south of the Paropamisus, and extending from the Heri-rud to the Sutlej and the mouths of the Indus, overstrained the strength of their State, and by shifting the centre of its power injured irretrievably its principle of cohesion. As early as the reign of Demetrius a tendency to disruption showed itself, Eucratidas having held the supreme power for many years in Bactria itself, while Demetrius exercised authority on the southern side of the mountains. It is true that at the death of Demetrius this tendency was to a certain extent checked, since Eucratidas was then able to extend his sway over almost the whole of the Bactrian territory. But the old evil recurred shortly, though in a less pronounced form. Eucratidas, without being actually supplanted in the north by a rival, found that he could devote to that portion of the Empire but a small part of his attention. The southern countries and the prospect of southern and eastern conquests engrossed him. While he carried on successful wars with the Arachotians, the Drangians, and the Indians of the Punjaub region, his hold on the more northern countries was relaxed, and they began to slip from his grasp. Incursions of the nomad Scyths from the Steppes carried fire and sword over portions of these provinces, some of which were Even, it is probable, seized and occupied by the invaders.