We left Mothanna, after the battle of Boweib, ravaging at pleasure the terror-stricken coasts of Chaldæa. In the alternations of war, another wave from the opposite quarter was about to sweep over that unhappy land. A new movement was taking place at Medâin. The Persian nobles, scandalised at the weakness of Rustem and the feeble Queen, began to cry out that he was dragging the empire down to ruin. The ladies of the court were assembled to inquire whether any king might not yet be discovered of the royal blood. At last there was found Yezdegird, saved as a child from the massacre of Siroes, and now a youth of twenty-one.[248] He was placed upon the throne. Around the young King the nobles rallied loyally, and something of the old fire of the empire was rekindled. Troops were gathered, Mesopotamia was reoccupied, and the cities as far as Hîra and the desert strongly garrisoned. [Sidenote: Mothanna forced to fall back. Dzul Cáda, A.H. XIII. January, A.D. 635.] The inhabitants returned to their ancient allegiance; and Mothanna, finding the whole Sawâd in arms, and his diminished army unable to cope with the rising, again withdrew, and concentrated his troops behind the Euphrates. He sent an urgent message, telling of the new perils threatening him, to Omar. The danger was met bravely by the Caliph. ‘I swear by the Lord,’ he cried, when the tidings reached him, ‘that I will smite down the princes of Persia with the sword of the princes of Arabia.’ It was clearly impossible to hold any part of Mesopotamia or the delta of the Euphrates, so long as they were dominated close at hand by the court of Persia on the banks of the Tigris. The capital must be taken at any cost, and an army large enough gathered for the purpose. [Sidenote: Omar orders another levy _en masse_.]Orders, more stringent even than those before, went forth (as we have already seen) for a new and universal levy. ‘Hasten to me,’ he wrote in all directions, ‘hasten speedily!’ And forthwith Arabia resounded again with the call to arms. The troops from the south were to gather before the Caliph at Medîna; those nearer to Syria, the demand being urgent and time precious, were to march straight to Mothanna. [Sidenote: Dzul Hijj. A.H. XIII. February, A.D. 635.] This much arranged, Omar set out on the annual pilgrimage to Mecca. On his return, he repaired to the rendezvous at Jorf, where the contingents as they came in were marshalled. In a council of war, it was debated whether the Caliph, as he proposed, and as the people wished, should in person lead the army to Irâc. The chief ‘Companions’ were against it.[249] Defeat, if Omar were on the field of battle, might be fatal; but seated at Medîna, even under the worst disaster he could launch column after column on the enemy. Omar yielded; and, whatever may have been his real intention the show of readiness to bear the heat and burden of the day imparted a new impulse of enthusiasm to the army. [Sidenote: Sád appointed commander in Irâc.]