In the same spirit, after the capture of the citadel of Khaibar, Kenana, the gallant Jewish prince, was put by the conquerors to the severest tortures, to induce him to confess where he had concealed his treasure; and when these failed to accomplish their purpose, his head was struck off with a sabre. But Mahomet narrowly escaped, at this time, feeling the vengeance of the Jewish people, by the act of a woman. On his arrival within the citadel, he required that some food should be served, and a shoulder of lamb was placed before him and his followers. But the first mouthful caused him severe internal pain; and though he instantly vomited forth what he had eaten, his system had imbibed so much of the poison which the meat had contained, as to cause him continual paroxysms of suffering during the remainder of his life. The Jewish woman by whom the lamb had been poisoned calmly avowed and justified the deed.[74] Her fate is uncertain. Having now attained the position of an independent potentate, Mahomet despatched letters to Heraclius, Chosroes, and the Governor of Egypt, inviting them to adopt his faith. By Chosroes these were received with scorn and anger; by the other two, we are told, with civility and feigned respect. Nevertheless, reports were brought that Heraclius was assembling an army for the purpose of crushing him; and it is probable that Mahomet would now have followed out what had long been his persistent purpose, and entered on the forcible conversion of neighbouring nations, if he had not felt the approaching decay of the powers of life. He did go so far as to assemble an army, and advance across the country to Tabuc; but the tidings brought him that the Syrians had collected large bodies of troops, and the experience of the battle of Muta, in which they had proved themselves formidable enemies, induced him to withdraw to Medina. But after his death, Abu Beker, the first Caliph, prepared to carry out without delay the programme of his predecessor. An army was sent into Irak, the ancient Chaldæa and Babylonia, under Khaled, called the ‘Sword of God,’ and one of the most able of the Moslem leaders, with orders to overrun and subdue Hira, Cufa, and Aila, all of them tributary kingdoms owning the suzerainty of Persia.[75] Khaled accomplished his task with astonishing rapidity and completeness; and when he was withdrawn to take the command in Syria, his successors followed up his victories, with but few reverses, into the very heart of Persia, won great battles, captured Modayn, Hamadan, and Istakan (the ancient Ctesiphon, Ecbatana, and Persepolis), and finally hunted down and slew the hapless Yezdegird. With him the Sassanian dynasty came to an end, and the whole of Persia, A.D. 651, submitted to the dominion of the Caliphs.