To the inhabitants of Spain the Arab conquest in the years from 711 to 716 came as a bolt from the blue. For the Arabs themselves, however, the overnmning of Spain was merely one phase in a long process of expansion. 1 It was an eminently profitable and successful phase, and the success came very rapidly; but in the process of expansion which had begun at least as early as 630 there had been comparable phases. During the reign of the caliph 'Umar (634-44) the embryonic Arab state—at this time an alliance of many, but not yet all, of the tribes of the Arabian peninsula—had defeated the Byzantine empire and wrested from it the provinces of Syria and Egypt, and had dealt such a crushing blow to the Persian empire that it ceased to exist, leaving what we now call Iraq and Persia to be occupied by the Arabs as soon as they could find men to hold them securely. And this was only a beginning. For about a century the Arabs continued to move onwards and outwards. One line of expansion was north-east along the golden road to Samarqand and beyond, and another south-east into the Indus valley, while in the west they progressed through the coast-lands of North Africa. The advance was not gradual but rather by a series of jumps. There were periods of quiescence and consolidation, when the Arabs paused in the face of some serious obstacle or in order to deal with internal tensions.