Tzachas Bey https://en.m.wikipedia.org/wiki/Tzachas a Turkic Muslim hellenophile warlord having for ambition to become Roman emperor and take Constantinople for this purpose he built a fleet wich woul achieve some success and allied the Pecheneg a at least partially Muslim Turkish tribe wich migrated to the Balkan and pillaged the ERE for a joint attack on Constantinople OTL Alexios managed to defeat the Pecheneg and nearly completely wipe the tribe in the battle of Levounion with the help of the Cuman another nomadic Turkic tribe before they could joint force . What if the Pecheneg won instead https://en.m.wikipedia.org/wiki/Battle_of_Levounion PoD could be the pecheneg army being not taken by surprise or even taking them by surprise and somewhat winning the battle ( thinked about the Cuman not allying the Roman but that could mean no battle in itself) most of the coalised army end up dead or routed . Emperor Alexios killed by a lucky arrow or by one of his opposent at home after his defeat . With most of the Byzantine army being wiped out in the Battle i could see Tzanchas and the Pecheneg take Gallipoli and go siege Constantinople the Thedososian wall will still be a big obstacle but if the Roman leadership following Alexios death is incompetent enough and fail to organize a defence (with some traitor and lucky event to the Turk ) I could see the city fall like in the 4 crusade . With Tzachas being hellenophile and specifically wanting to be a Roman emperor I could see him creating a hellenized Islamic Roman Empire and attire thousand of Islamic Turkic adventurer at his command . But that just one of the possibility the siege could also fail . Now what I could see happening in either case after the victory at Levounion his the Petcheneg settling in the western Balkan thrace western Bulgaria southern Romania etc ... Bulgars rebellion the Norman profiting of the Byzantine weakness to take part of the Balkan some Roman rump state being created and Tzachas in the rest of his life if he doesn’t remain assassined like OTL wich he would probably do continu to renforce his principality and navy to retry a siege of Constantinople . Also the Pope upon learning of the siege of Constantinople would probably want to send a crusade analogue but it will take years to be prepared and arrive . What are the plausibility of that ? And your through ?