The new-born creed soon showed its strongly militant character. Led by Khālid, a pillar of Islām who won by his prowess the title of the Sword of God, the Arabs defeated a Roman army with heavy loss, and took Damascus. In six years the whole of Syria and Palestine passed under their sway. Persia was the next object of attack. The Zoroastrians struggled long and desperately for their independence, but in 639 they suffered a crushing defeat at Nahāvend, a battle which must rank high amongst those which have influenced the current of the world’s history. Yezdijerd, the last of the Sāsānian dynasty, fled through Sīstān and Khorāsān to Merv. Here he found no safe asylum, for the governor sent news of his arrival to the Turks, and the Khākān advanced in person to seize so rich a prize. The fugitive became aware of the intended treachery, and concealed himself in a mill near the city. The owner received him with apparent kindness, but was tempted by the splendour of the king’s accoutrements to kill him while he slept. He severed Yezdijerd’s head from his body, which he cast into the mill stream.[79] [Illustration: THE RAHLA, OR READING-DESK OUTSIDE THE MOSQUE OF BĪBĪ KHĀNŪM, SAMARKAND] The immediate results of the battle of Nahāvend were disastrous to civilisation. Persia was traversed in all directions by bands of marauding Arabs, and the miserable inhabitants suffered as severely as they had suffered at the hands of the Mazdakites. “The Caliph Othman,”[80] writes Gibbon,[81] “promised the government of Khorāsān to the first general who should enter that large and populous country, the kingdom of the ancient Bactrians. The condition was accepted, the prize was deserved; the standard of Mahomet was planted on the walls of Herāt, Merou, and Balkh; and the successful leader neither halted nor reposed till his foaming cavalry had tasted the waters of the Oxus.” The ill-cemented power of the Caliph was more adapted for conquest than assimilation, and its area overrun by his undisciplined hordes was too vast to be held in permanent subjection. Conscious of their weakness, the Arabs spared no efforts to spread the tenets of Islām, which alone was capable of welding together communities differing widely in race, language, and customs. From this epoch dates the decline of the creed of Zoroaster throughout Persia and the countries of Central Asia. The assassination of the Caliph `Omar by a Persian slave was the signal for a general insurrection throughout this loosely knitted empire. This was not finally quelled till A.H. 31 (652), when Ibn `Āmir gained a victory over the Persians at Khwārazm on the Oxus, and compelled the country as far as Balkh to acknowledge the Caliph’s suzerainty.[82] In A.H. 41 (661) `Abdullah ibn `Āmir organised a successful expedition into Khorāsān and Sīstān;[83] and in the course of the following year Kays ibn al-Haytham was sent thither as provincial governor. He was superseded in A.H. 43 (663) by `Abdullah ibn Khāzim. In A.H.