<Li> When I am dead allow me to be buried in the Church of St. John at Alexandria . </Li> <P> This position was to the advantage of the Muslims, as the Copts were the natives of the land of Egypt and both the Byzantines and the Muslims were strangers . </P> <P> The Byzantine commanders knew that the next target of the Muslims would be Alexandria . They accordingly prepared for the expected siege of the city . Their strategy was to keep the Muslims away from Alexandria by destroying their power through continued sallies and attacks from the fort . Even if this did not keep them away, it would weaken them morally and physically . It would be more of a war of patience than strength . In February 641,' Amr set off for Alexandria from Babylon with his army . All along the road from Babylon to Alexandria, the Byzantines had left regiments to delay, and if possible, inflict losses on the advancing Muslims . On the third day of their march from Babylon the Muslims' advance guard encountered a Byzantine detachment at Tarnut on the west bank of the Nile . The Byzantines failed to inflict heavy losses, but they were able to delay the advance by one more day . The Muslim commanders decided to halt the main army at Tarnut and send the advance guard cavalry forward to clear the way from the possible Byzantine detachments . This was done so that the main army could reach Alexandria as soon as possible without being delayed by Byzantine regiments mid-way . Thirty kilometres (20 mi) from Tarnut, the Byzantine detachment that had withdrawn from Tarnut the day before, joined the detachment already present at Shareek to form a strong offensive force . They attacked and routed the Muslim advance guard . The next day, before the Byzantines could resume their offensive to annihilate the Muslim advance guard completely, the main Muslim army arrived, prompting the Byzantines to withdraw . At this point the Muslim commanders decided not to send forward the advance guard, so the whole army marched forward, beginning the following day . The Muslims reached Sulteis where they encountered a Byzantine detachment . Hard fighting followed, but the Byzantine resistance soon broke down and they withdrew to Alexandria . The Muslims halted at Sulteis for a day . Alexandria was still two days' march from Sulteis . After one day's march the Muslim forces arrived at Kirayun, twenty kilometres (12 mi) from Alexandria . Here the Muslim advance to Alexandria was blocked by a Byzantine detachment about 20,000 strong . The strategy of the Byzantines was that either the Muslims would be driven away before they actually arrived at Alexandria, or that they would be as weak as possible if they did . The two armies were deployed and fighting followed, but action remained indecisive, . This state of affairs persisted for ten days . On the tenth day the Muslims launched a vigorous assault . The Byzantines were defeated and they retreated to Alexandria . The way to Alexandria was now cleared, and the Muslim forces resumed the march from Kirayun and reached the outskirts of Alexandria in March 641 AD . </P> <P> The Muslims laid siege to Alexandria in March 641 AD . The city was heavily fortified: there were walls within walls, and forts within forts . There was no dearth of provisions and food supply in the city . The city also had direct access to the sea, and through the sea route help from Constantinople in the form of men and supplies could come at any time . </P>

When did egypt break away from the abbasid caliphate