Having killed and succeeded his father, Sheroye—crowned as Kavadh II—made peace with Heraclius; surrendered Egypt, Palestine, Syria, Asia Minor, and western Mesopotamia; returned to their countries the captives taken by Persia; and restored to Jerusalem the remains of the True Cross. Heraclius reasonably rejoiced over so thorough a triumph; he did not observe that on the very day in 629 when he replaced the True Cross in its shrine a band of Arabs attacked a Greek garrison near the River Jordan. In that same year pestilence broke out in Persia; thousands died of it, including the King. His son Ardashir III, aged seven, was proclaimed ruler; a general, Shahr-Baraz, killed the boy and usurped the throne; his own soldiers killed Shahr-Baraz, and dragged his corpse through the streets of Ctesiphon, shouting, “Whoever, not being of royal blood, seats himself upon the throne of Persia, will share this fate”; the populace is always more royalist than the king. Anarchy now swept through a realm exhausted by twenty-six years of war. Social disintegration climaxed a moral decay that had come with the riches of victory.68 In four years nine rulers contested the throne, and disappeared through assassination, or flight, or an abnormally natural death. Provinces, even cities, declared their independence of a central government no longer able to rule. In 634 the crown was given to Yezdegird III, scion of the house of Sasan, and son of a Negress.69
In 632 Mohammed died after founding a new Arab state. His second successor, the Caliph Omar, received in 634 a letter from Muthanna, his general in Syria, informing him that Persia was in chaos and ripe for conquest.70 Omar assigned the task to his most brilliant commander, Khalid. With an army of Bedouin Arabs inured to conflict and hungry for spoils, Khalid marched along the south shore of the Persian Gulf, and sent a characteristic message to Hormizd, governor of the frontier province: “Accept Islam, and thou art safe; else pay tribute. … A people is already upon thee, loving death even as thou lovest life.”71 Hormizd challenged him to single combat; Khalid accepted, and slew him. Overcoming all resistance, the Moslems reached the Euphrates; Khalid was recalled to save an Arab army elsewhere; Muthanna replaced him, and, with reinforcements, crossed the river on a bridge of boats. Yezdegird, still a youth of twenty-two, gave the supreme command to Rustam, governor of Khurasan, and bade him raise a limitless force to save the state. The Persians met the Arabs in the Battle of the Bridge, defeated them, and pursued them recklessly; Muthanna re-formed his columns, and at the Battle of El-Bowayb destroyed the disordered Persian forces almost to a man (624). Moslem losses were heavy; Muthanna died of his wounds; but the Caliph sent an abler general, Saad, and a new army of 30,000 men. Yezdegird replied by arming 120,000 Persians. Rustam led them across the Euphrates to Kadisiya, and there through four bloody days was fought one of the decisive battles of Asiatic history. On the fourth day a sandstorm blew into the faces of the Persians; the Arabs seized the opportunity, and overwhelmed their blinded enemies. Rustam was killed, and his army dispersed (636). Saad led his unresisted troops to the Tigris, crossed it, and entered Ctesiphon.
The simple and hardy Arabs gazed in wonder at the royal palace, its mighty arch and marble hall, its enormous carpets and jeweled throne. For ten days they labored to carry off their spoils. Perhaps because of these impediments, Omar forbade Saad to advance farther east; “Iraq,” he said, “is enough.”72 Saad complied, and spent the next three years establishing Arab rule throughout Mesopotamia. Meanwhile Yezdegird, in his northern provinces, raised another army, 150,000 strong; Omar sent against him 30,000 men; at Nahavand superior tactics won the “Victory of Victories” for the Arabs; 100,000 Persians, caught in narrow defiles, were massacred (641). Soon all Persia was in Arab hands. Yezdegird fled to Balkh, begged aid of China and was refused, begged aid of the Turks and was given a small force; but as he started out on his new campaign some Turkish soldiers murdered him for his jewelry (652). Sasanian Persia had come to an end.