In the mean time, the approach of danger had reunited the Mussulman princes. The caliph of Bagdad, whom James of Vitri[218] styles _the pope of the infidels_, exhorted the nations to take up arms against the Christians. All the sons of Malek-Adel, who reigned over the provinces of Syria and of Yemen, prepared to march to the assistance of Egypt. The sultan of Damascus, after having made several incursions into the territories of Ptolemaïs, gathered together his whole army, and resolved to go and defend Damietta. As he had reason to fear the Christians might take advantage of his absence to seize Jerusalem and fortify themselves in it, he caused the ramparts of the holy city to be demolished. He also ordered the fortress of Tabor, and all those that the Mussulmans held along the coasts of Palestine, to be destroyed; a vigorous measure that afflicted the infidels, but was calculated to afflict the Christians still more; as it proved to them that they had to contend with enemies animated by despair, and disposed to sacrifice everything to secure their own safety. The sultan of Cairo encamped in the vicinity of Damietta, where he awaited the princes of his family. The garrison of the city received every day provisions and reinforcements, and was in a condition to resist the Christian army for a length of time. The preparations and the approach of the Mussulmans at length roused the Crusaders from their state of inaction. Animated by their leaders, but more by the appearance of danger and the presence of a formidable enemy; still led by the king of Jerusalem, who had resisted the pretensions of Pelagius, the Christian soldiers resumed the labours of the siege and made several assaults upon the city on the river side. The winter, which had just set in, did not at all prevent their attacks; nothing could equal the heroic constancy with which they braved, during several months, cold, rain, hunger, all the fatigues of war, and all the rigours of the season. A contagious malady committed great ravages in the Christian army: a frightful storm, which lasted three days, carried away the tents and the baggage of both leaders and soldiers; but nothing diminished the fury of the contests, which were incessantly renewed. At length the Christians, having become masters of all the western bank of the Nile, determined to cross the river, and attack the city on the land side. The passage was difficult and dangerous; the sultan of Cairo had fixed his camp on the opposite shore; the plain on which the Crusaders wished to pitch their tents was covered with Mussulman soldiers; an unexpected event removed all obstacles.