The siege of Montreal (21 September-October 1171) was a controversial episode of the career of Saladin after he lifted the siege, probably because his overlord Nur ad-Din was approaching with a second army.
In September 1171 Saladin, who had been in power in Egypt since 1169, finally deposed the last Shiite Fatimid caliph (just before he died of natural causes). Almost immediately he left Cairo to launch an attack on the Crusader castle at Montreal (ash-Shaubak), south of the Dead Sea. This attack was probably carried out in response to orders from Saladin's overlord, Nur ad-Din, the ruler of Syria. Nur ad-Din also prepared an army ready to take part in the siege.
This was a good moment to attack Montreal. King Amalric of Jerusalem was in Constantinople, arranging an alliance with the Emperor Manuel Comnenus, so the kingdom was missing its most able leader.
Saladin arrived outside Montreal on 21 September 1171. The Crusader castle was much smaller than the existing ruins, which are of a later castle. The defenders were caught out, and requested a ten-day long armistice, presumably in the hope that a relieving army could be raised in the Crusader kingdom.
A relief army did appear, but it came from a most unexpected source. When Saladin discovered that Nur ad-Din was approaching he decided to lift the siege and return to Egypt. His official excuse was a revolt in Upper Egypt, but with the castle about to fall and Saladin's capable brothers dealing with the revolt, this didn’t ring true. Saladin was probably more concerned that Nur ad-Din would replace him as vizier of Egypt.
After this snub Nur ad-Din probably considered leading his army into Egypt. Many of Saladin's captains were in favour of resisting any such attack, but Saladin's father Ayyub gave him better advice. In public he recommended that Saladin offer all signs of loyalty to Nur ad-Din, as none of his troops would be willing to fight their official overlord. In private Ayyub's advice was similar, but he is said to have pointed out that Saladin was the younger man, and so time was on his side. Saladin was able to placate Nur ad-Din, and was still in place in Egypt when Nur ad-Din died in May 1174.