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
In 284 following the deaths of Emperors Carus (struck by lightning) and Numerian (By illness or assassination) in Persia... army elected Flavius Diocles as Emperor under the name of Diocletian (Flavius Aper was the front runner for the Purple but he was accused for the murder of young Numerian by Diocles and was slain by him before he could defend himself)
In May 285 Diocletian confronted Carinus son of the late Emperor Carus in the battle of Margus... Carinus was winning the battle when his Praetorian Praefect Aristobulus and his Praetorians deserted to Diocletian and Aristobulus backstabbed Carinus leaving Diocletian sole Emperor...
WI Aristobulus doesnt deserts and Carinus wins the Battle? Tetrarchy is butterflied away for sure... so is the rise of Christianity... And NO Dominate era... Could the Principate had survived?
Also (in my opinion) slow hellenisation (sic) of the Empire is delayed significantly... so no Byzantine Empire for 200-300 years at most...