Amru lost no time in marching upon Alexandria, so as to reach it before the Greek troops, hastily called in from the outlying garrisons, could rally there for its defence. [Sidenote: capitulates A.H. XX. A.D. 641.]On the way he put to flight several columns which sought to hinder his advance; and at last presented himself before the walls of the great city, which, offering (as it still does) on the land side a narrow and well-fortified front, was capable of an obstinate resistance. Towards the sea also it was open to succour at the pleasure of the Byzantine Court. But during the siege, Heraclius died, and the opportunity of relief was supinely allowed to slip away.[371] Some of the protective outworks on the narrow isthmus were taken by storm; and there appearing no prospect of support from Constantinople, the spirit of the garrison began to flag. The Greeks took to their ships, and in great numbers pusillanimously deserted the beleaguered city. At last Mucoucus, who after his defeat had retired to Alexandria, finding the place too weak for a prolonged defence, offered to capitulate, on the same terms as were given to Upper Egypt, and on condition that the prisoners taken throughout the campaign were set free. The Caliph, being referred to, readily agreed. ‘Tribute,’ he replied, ‘is better than booty; for it continueth, whereas spoil soon vanisheth as if it had not been. Touching the captives, such as are already scattered, are beyond my power; but those that remain, saving such as were seized on the field of battle, shall be restored.’ And so the city escaped sack, and the people became tributary to the conquerors.[372] [Sidenote: Amru founds _Fostât_, or Cairo.] Amru, it is said, wished to fix his seat of government at Alexandria, but Omar would not allow him to remain so far away from his camp, with so many branches of the Nile between. So he returned to Upper Egypt. A body of the Arabs crossed the Nile and settled in Ghîzeh, on the western bank--a movement which Omar permitted only on condition that a strong fortress was constructed there to prevent the possibility of their being surprised and cut off.[373] The head-quarters of the army were pitched near Memphis. Around them grew up a military station, called from its origin FOSTÂT, or ‘the Encampment.’ It expanded rapidly into the capital of Egypt, the modern Cairo.[374] And there Amru laid the foundations of a great Mosque, which still bears his name. [Sidenote: The soil left in the hands of the cultivators.]