A Roman Empire TL created and written by Janus Antoninus, starting with the death of Commodus after his father had adopted an orphan boy. Written over the course of six years on another wiki as Superpowers.
In tackling the common task of making Rome retain its dominion over Europe, the core idea of this TL is to explore the history of the kind of Rome that could survive into its Sæculum Novum. The Roman Empire could not have survived as it had been during the Nerva-Antonine period and beyond; an empire that survives long past its historical decline must have reforms of its political structures and rules in a different direction than IOTL. There are perhaps a number of ways this could occur but this TL develops one such possibility.
165 AD: Birth of Gaius Correlus Sulla to Roman colonists in the city of Athens.
Orphaned by the Antonine plague, Gaius develops the skills to survive on his own for several years. On a tour of Greece, Marcus Aurelius is approached by this boy after speaking to an audience at the Stoa Poikile, where Gaius had listened keenly to this man who was being shown great respect by the entire crowd. Bearing a resemblance to the late Annius Verus, Sulla further drew the attention of the emperor with a demonstration of his keen memory for the speeches made by philosophers throughout Athens. For private rather than public reasons, Marcus Aurelius adopts this curious youth and begins to spend time with him as he never could with the son he had lost nor with the son he was responsibly grooming in Rome for the succession.
Growing closer to his adopted son, Marcus Aurelius decides that he would make a worthy emperor alongside Commodus - as Lucius Verus had been next to Marcus in a bygone era. When Commodus dies, seemingly from the plague, shortly thereafter, Sulla is left as the sole successor. On the untimely death of Marcus Aurelius, the boy of humble birth is recognized by the Senate as Caesar Gaivs Aurelivs Antoninvs Svlla Augustus and takes up the burden of his adoptive father. The rest, as they say, is history.