The author of the Armenian history attributed to Sebeos records the year 651 as the twentieth of the reign of the Persian Shah Yazkert, the eleventh of the Roman Emperor Constans and the nineteenth of the dominion of the Ismaelites. He then narrates how it was in this year that the Persian Empire was subsumed within the expanding Islamic polity, and the Sasanian dynasty came to an end after a period of 542 years. The figure is slightly mistaken—in fact Sasanian rule had lasted 425 years since the ascension of Artashir I in AD 226. Nevertheless it is an error that well illustrates the perceived antiquity of the old order, in which one great empire dominated the Mediterranean basin and another the Iranian plateau. The Arab conquests of the mid seventh century permanently erased this division. Until the Abbasid Revolution of AD 750/132 AH the capital of the new Caliphate would be located at Damascus, well within formerly Roman territory and in a commanding position from which to control the waters of the Eastern Mediterranean. Islamic armies annually raided deep into Roman territory and made attempts to capture Constantinople in AD 653-54, 674-78, 716-18 and 782. In The Empire That Would Not Die, a project growing out of four Carl Newell Jackson lectures delivered at Harvard in 2014, John Haldon asks how it was that the Roman state survived in the face of a hostile neighbour that was larger, qualitively more prosperous and determined to expand.