Does everyone realize how screwed Byzantium was by 1444? It was basically an Ottoman vassal state, forced to pay tribute, etc. Needed Ottoman permission to be crowned, had devolved from the once resplendent city into really a collection of villages, separated by their own palisades. Even the palace of Blachernae was just a shadow of its former glory. The Theodosian Walls, which had stood defiant to even the greatest armies, where in ill repair. At coronations, the feast was served on clay and pewter plates, the crown jewels actually glass, having been sold to pay for bankrupting civil wars. The combined forces of Byzantium numbered some 4,000 (in 1453 an additional 4,000 Latins came to help). Constantine XI, upon succession, had to beg his way to afford passage on a boat back to the capital...yeah. Ottomans, meanwhile, numbered somewhere between 80,000 and 160,000, where richer, technologically superior, better trained (the Hungarians knew all too well). Basically, starting as the Romans should be quite nearly impossible.