User blog comment:Daltonb1993/Byzantine Assassin/@comment-4043223-20110822011838

It is unknown as of yet why the Byzantines forces were fighting alongside Altair at the time but given it occured over 400 years before Ezio's time then it isn't to far beyond the realm of possibility that they were allies to the Assassins. Remember from the books that Altair tried to establish a guild in Constantinople around that time, which was a time when the Byzantines had a firm hold on the region unlike when Revelations takes place.