The first invasion took place under Khalif Omar (633). [6] Khalud Ben Walid at the head of ten thousand men, and Mosanna at the head of eight thousand, had marched against Hormuz, the Persian Governor of Irak, and had vanquished him. After this victory Khalud had gone forward and conquered Irak; but he was defeated at the battle of Marwaha (634). Four thousand Mussulmans were killed, and two thousand returned to Medina. Unfortunately the Persian general Behman did not follow up this advantage. The country was at this time divided into two factions, one under Rustam, the generalissimo of the Persian Empire, the other under Prince Firoz. Behman, instead of securing the independence of his country, hastened to support Rustam against Firoz. The Arabs, emboldened by their rapid successes, established their camp between Kadesia [7] and Koufah, where by the Caliph's order hordes of Nomads came to reinforce their troops. The struggle lasted for three days and three nights; the Persian army was entirely destroyed, and the royal standard fell into the hands of the Arabs. [8] Yezdezard, informed of this misfortune, escaped to Holwan. Sa'd, having taken possession of Madain, pursued the fugitive monarch, who withdrew to Rei. In the twentieth year of the Hejira, Omar recalled Sa'd, and Yezdezard took this opportunity to gather together a hundred and fifty thousand men, all the contingents having been drawn from the province of Khorassan and from the environs of Rei and Hamadan. Firouzan was appointed commander. The Caliph, hearing of the preparations of the Persian king, sent in his turn reinforcements, and placed at their head his general No'man, with the strictest orders to destroy the impious religion of the Fire-Worshippers. It was at Nehawend [9] that, after a delay of two months, the shock of arms decided the fate of Iran. Thirty thousand Persians fell on the battlefield, and eighty thousand were drowned in the moats surrounding the camp. Firouzan was pursued into the mountains and killed by a detachment of Arabs. [10] From that time Persia passed into the hands of the Caliphs. Yezdezard escaped at first to Seistan and then to Merv. The governor of this town offered to deliver up the fugitive prince to the Khan of Turkestan. The Turks entered the town in spite of the resistance of the inhabitants, and the king, taking advantage of the confusion, succeeded in hiding himself in a neighbouring mill. The miller at first gave protection to the king; but urged by a desire to get possession of his arms and his clothes, he, like a coward, killed the king. The irate people massacred the assassin, and the body of Yezdezard, son of Sheheriar, the last sovereign of the Sassanian dynasty, was sent to Istakhr, there to be deposited in the tomb of his ancestors (A.D. 650).