After Câdesîya and the loss of Medâin, Yezdegird may have buoyed himself up with the hope that the Arabs, content with the fertile plains of Mesopotamia and Irâc-Araby, would leave him in undisturbed possession of the ample provinces of Persia proper beyond the mountain range. But the capture of the ancient capital of Media, and the threatening advance of the invaders in the direction of Ispahan and Persepolis, put an end to any such imagination. Teeming, restless hordes, still issuing from the Peninsula, began to press upon the border; and their irruption into the farther plains of Persia became clearly a mere question of time. The king, therefore, resolved once more upon a grand effort to stem the tide of invasion. With this view he ordered the governors of the various provinces to gather their forces together for a final attack. These, especially in the outlying regions, appear to have enjoyed an almost independent authority. But their interests were now knit together by the common danger. From the shores of the Caspian, therefore, to the Indian Ocean, and from the Oxus to the Persian Gulf, they rallied around the royal standard, and in vast number gathered on the plain that lies below the snow-capped peak of Demavend. [Sidenote: Omar sends an army under Nómân to oppose them.] Tidings of the movement soon reached Kûfa, and Sád apprised the Caliph of the rising storm. Each courier, as he arrived, filled the city with fresh alarms. A hundred and fifty thousand men had assembled under Firuzân; now they were encamped at Hamadan, and now marching on Holwân; they would soon be close to Kûfa, and at their very doors. The crisis, no doubt, was serious. Any reverse to the Arabs on the mountain border would loosen their hold upon the plains below; and all the conquests in Chaldæa, with Medâin, and the settlements even of Kûfa and Bussorah, might be wrenched from their grasp. As on previous occasions of imminent danger, Omar at once declared his resolve to march forth in person. Encamped midway between the two cities of Irâc, his presence would restore confidence; and while able from thence to direct the movements in front, his reserve would be a defence to them in the rear. But the old arguments against leaving Medîna again prevailed, and Omar was persuaded to remain behind.[389] Nómân was recalled from the campaign just described for the reduction of Khuzistan, to take the chief command. Leaving strong garrisons behind, all available troops were pushed forward in two columns from Bussorah and Kûfa. The army at Sûs, besides furnishing a contingent for the main advance, was given the important task of effecting a diversion by an attack upon Persepolis, and so preventing the native forces in that quarter from joining the royal standard. [Sidenote: Battle of Nehâvend. A.H. XXI. A.D. 642.]