It is enough, for our present purpose, to know that in neither of the two great powers had the nerve and virtue of early days survived. [Sidenote: Roman and Persian empires at Mahomet’s death.]Luxury, oppression, religious strife, and military disaster had undermined their strength and impaired their vigour. The Roman empire, extinguished in the west by barbarian hordes, existed only in the provinces governed by the Byzantine capital. Between the Kaiser and the Chosroes war had long prevailed; and Syria or Mesopotamia had been the prize now of one, now of the other. By the last turn of fortune, Heraclius, in a brilliant campaign directed from the Black Sea, had routed the Persians on the field of Nineveh, and marched triumphantly to the very gates of Ctesiphon (_Medâin_). [Sidenote: A.H. VI. A.D. 627.] The Chosroes, with eighteen of his sons, was put to death by Siroes, who enjoyed but a few months the fruit of his parricidal crime; and ‘in the space of four years, the royal title was assumed by nine candidates, who disputed, with the sword or dagger, the fragments of an exhausted monarchy.’[96] Such was the condition of Persia, its court imbecile and anarchy rampant, at the time when Abu Bekr was engaged in his struggle with the apostate tribes. Nevertheless, the Arabian armies met with a fiercer and more protracted opposition on the Persian than on the Syrian side. And the reason is that Islam aimed its blow at the very heart of Persia. Constantinople might remain, with Syria gone, ignobly safe. But if the Arabs gained Irâc, Ctesiphon must fall into their hands. [Sidenote: Mothanna attacks the border tribes of Irâc.] Among the chiefs who aided Alâ in the reoccupation of Bahrein, Mothanna has been named.[97] Advancing up the shore of the Persian Gulf, he reduced Catîf, and carried his victorious army into the delta of the Euphrates. ‘Who is this Mothanna?’ asked Abu Bekr, as tidings of his success kept reaching Medîna; ‘and to what tribe doth he belong?’ Learning that he was of the Beni Bekr ibn Wâil, he gave him a commission to carry forward his arms, fighting in the ways of the Lord.[98] The service was just such as the Arabs loved; and Mothanna’s column was soon swelled to 8,000 men. But opposition gathered in front. The Christian and heathen tribes were roused; and Abu Bekr, anticipating a struggle strongly backed by other forces in their rear, resolved that (Khâlid being now at leisure) ‘the Sword of the Lord’ should be unsheathed there. [Sidenote: Abu Bekr sends troops under Khâlid and Iyâdh towards Irâc. A.H. XII. March, A.D. 633.]