THE PRE-ISLAMIC PHASE of west Eurasian history came to a violent close in the first third of the seventh century. The two established great powers, the East Roman empire centred on the Mediterranean and its continental adversary, the Sasanian empire, fought their last, longest and most ferocious war. This war deserves attention for its dramatic qualities. It is framed by two coups d'état, while a third had a decisive influence on its course, opening the way for Sasanian armies to reach the sea and to split the Roman Near East in two; the nomad powers of the north, Turks and Avars, were drawn into the fray in its third and final phase, successively imperilling each of the southern empires; and fortune finally abandoned the forces of the shah Khusraw Abarvez and allowed the Roman emperor, Heraclius, to gamble all on one bold final throw, fraught with danger, and to win.

Victory came on the night of 23-24 February 628 when Khusraw was deposed in a carefully planned and well executed operation. The new shāhanshāh, Khusraw's eldest son Kawadh Shiroe, forthwith pro- posed an armistice and inaugurated peace negotiations. He was dead by the time peace-all too ephemeral a peace-finally took hold two years later and the traditional equilibrium was apparently restored be- tween the great powers. Within ten years, though, both empires suffered shattering defeats in the field at the hands of the umma created by Muḥammad. Within a generation, the eastern power was swallowed whole by the nascent Muslim state, while the western was stripped of all its rich Near Eastern provinces and only succeeded in clinging to Anatolia by investing all its energies in a guerrilla war of defence.

The juxtaposition of the last great war of antiquity and the Arab conquests has naturally led historians to connect them causally. While Palestine and Syria, with a long, open frontier facing the desert, were indefensible against substantial forces deployed against them from deep within Arabia, especially if those forces were well-motivated, the same was not true of the Mesopotamian alluvium which formed the economic and political heartland of the Sasanian empire. Its desert frontier was much shorter than that of the Roman Near East and possessed a natural line of defence in the Euphrates, which was itself shielded by a number of forward bases.