The siege of Alexandria of 29 July- 2 August 1174 was a brief and very unsuccessful attempt by the Normans of Sicily to play a part in the overthrow of Saladin, then vizier of Egypt.
In 1169 Saladin had become vizier and commander-in-chief of the Egyptian army, a position that meant he was officially working both for his own master, the Sunni Nur-ad-Din and for the Fatimid caliph in Cairo, a Shiite. The Crusaders quickly realised the danger posed by a united Moslem world, and attempted to intervene, attacking Damietta (25 October-19 December 1169). This attack was repulsed, and in 1170 Saladin went onto the offensive himself, capturing Ayla at the head of the Gulf of Aqaba.
In 1171 Saladin finally substituted the name of the orthodox Sunni caliph for that of the Fatimid caliph in the prayers in the mosques of Cairo, announcing the return to orthodoxy in Egypt. The last caliph died a few days later, of natural causes and probably without ever knowing that he had been overthrown. At first the surviving members of the Fatimid elite stayed quiet, but by 1174 they had decided to revolt.
The plan was for a multi-pronged assault on Saladin. There would be a revolt in Cairo and another revolt at Aswan in the far south. The Egyptians returned to their almost traditional policy of allying with the Crusaders, and arranged for two attacks. One would come from Jerusalem, led by king Amalric while the second would be a naval attack on Alexandria, to be carried out by the Normans of Sicily, then one of the main naval powers in the Mediterranean.
The plot fell apart before it could begin. In March Saladin's men uncovered the plot in Cairo. The chief plotters were arrested, and in April they were executed. Amalric died in July, removing the last truly effective King of Jerusalem. The revolt in Aswan remained undetected, but by the time the news reached Saladin the threat to Alexandria was already over.
The Sicilian threat was still a serious one. King William II collected a large fleet, which Ibn al-Athir described as containing 200 warships forty supply ships, 1,500 cavalry, 30,000 infantry and six ships full of siege engines. Other sources agree on the size of the fleet although differ slightly on the size of the army.
This sounds like an impressive army, but the Sicilians had expected that Saladin would be distracted by revolts and by Amalric. Instead he was close to Alexandria and ready to intervene. The port was blocked with sunken ships. The Sicilians were able to land, and assembled either three or six massive siege towers, and three heavy catapults. These greatly impressed the defenders of the city, but they were less impressed with the organisation of the Sicilian army.
On the third day of the siege the defenders sallied from the city gates and caught the Sicilians by surprise. The siege towers were destroyed and most of the besieging troops fled to their ships. Three hundred horsemen were isolated and had to dig in on top of a hill, before later being overwhelmed. On 2 August the Sicilians abandoned the siege, and sailed away. William of Tyre extends the siege to five or six days, but the result was the same.
In some versions of the siege the sortie was on the third day and the final fighting and the isolation of the 300 took place when Saladin's field army arrived. In others the sortie and the final battle both took place on the third day of the siege. The sortie came first, and the defenders attacked a second time on the same day when a messenger arrived from Saladin to announce that his army was close by.
Only now did news arrive of the revolt in the south. This was soon under control, and Saladin was finally free to take advantage of news that had arrived from Syria - in May Nur ad-Din had died, and while Saladin was defending Egypt the unity of Syria collapsed. Saladin was invited to take over at Damascus. Once the revolts had been out down he left Cairo heading for Syria and the campaigns that would secure him as an independent ruler of Damascus and Egypt.