structural:reformatting, quality:correction, structural:scholar_edition
Alliance with the Kingdom of Jerusalem

Control of Egypt was a decades-old dream of the crusader Kingdom of Jerusalem, and its king Amalric I needed all the military and financial support he could get for his planned campaign. Amalric also realised that if he were to pursue his ambitions in Egypt, he might have to leave Antioch to the hegemony of Manuel, who had paid 100,000 dinars for the release of Bohemond III. In 1165, he sent envoys to the Byzantine court to negotiate a marriage alliance (Manuel had already married Amalric's cousin Maria of Antioch in 1161). After a long interval of two years, Amalric married Manuel's grandniece Maria Komnene in 1167, and "swore all that his brother Baldwin had sworn before." A formal alliance was negotiated in 1168, whereby the two rulers arranged for a conquest and partition of Egypt, with Manuel taking the coastal area, and Amalric the interior. In the autumn of 1169 Manuel sent a joint expedition with Amalric to Egypt: a Byzantine army and a naval force of 20 large warships, 150 galleys, and 60 transports, under the command of the megas doux Andronikos Kontostephanos, joined forces with Amalric at Ascalon. William of Tyre, who negotiated the alliance, was impressed in particular by the large transport ships that were used to transport the cavalry forces of the army.

Although such a long-range attack on a state far from the centre of the Empire may seem extraordinary (the last time the Empire had attempted anything on this scale was the failed invasion of Sicily over one hundred and twenty years earlier), it can be explained in terms of Manuel's foreign policy, which was to use the Latins to ensure the survival of the Empire. This focus on the bigger picture of the eastern Mediterranean and even further afield thus led Manuel to intervene in Egypt: it was believed that in the context of the wider struggle between the crusader states and the Islamic powers of the east, control of Egypt would be the deciding factor. It had become clear that the ailing Fatimid Caliphate of Egypt held the key to the fate of the crusader states. If Egypt came out of its isolation and joined forces with the Muslims under Nur ad-Din, the crusader cause was in trouble.

A successful invasion of Egypt would have several further advantages for the Byzantine Empire. Egypt was a rich province, and in the days of the Roman Empire it had supplied much of the grain for Constantinople before it was lost to the Arabs in the 7th century. The revenues that the Empire could have expected to gain from the conquest of Egypt would have been considerable, even if these would have to be shared with the Crusaders. Furthermore, Manuel may have wanted to encourage Amalric's plans, not only to deflect the ambitions of the Latins away from Antioch, but also to create new opportunities for joint military ventures that would keep the King of Jerusalem in his debt, and would also allow the Empire to share in territorial gains.