You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
So let's assume that the Byzantines are able to re-conquer the Levant around about the OTL Crusade period. They do not however regain Egyty. How well can the Byzantines hold the region and would holding the Levant do much to improve the Byzantine's ability to hold out against their neighbours?