From these successful inroads the Romans derived no real or lasting benefit; nor did they attempt to preserve such distant conquests, separated from the provinces of the empire by a large tract of intermediate desert. The reduction of the kingdom of Osrhoene was an acquisition of less splendor indeed, but of a far more solid advantage. That little state occupied the northern and most fertile part of Mesopotamia, between the Euphrates and the Tigris. Edessa, its capital, was situated about twenty miles beyond the former of those rivers; and the inhabitants, since the time of Alexander, were a mixed race of Greeks, Arabs, Syrians, and Armenians. The feeble sovereigns of Osrhoene, placed on the dangerous verge of two contending empires, were attached from inclination to the Parthian cause; but the superior power of Rome exacted from them a reluctant homage, which is still attested by their medals. After the conclusion of the Parthian war under Marcus, it was judged prudent to secure some substantial pledges of their doubtful fidelity. Forts were constructed in several parts of the country, and a Roman garrison was fixed in the strong town of Nisibis. During the troubles that followed the death of Commodus, the princes of Osrhoene attempted to shake off the yoke; but the stern policy of Severus confirmed their dependence, and the perfidy of Caracalla completed the easy conquest. Abgarus, the last king of Edessa, was sent in chains to Rome, his dominions reduced into a province, and his capital dignified with the rank of colony; and thus the Romans, about ten years before the fall of the Parthian monarchy, obtained a firm and permanent establishment beyond the Euphrates.