This timeline is Open For Adoption, feel free to adopt and expand it.
For details see Adoption Policy
Marcus Aurelius adopts a suitable general named Julius (who was born ATL 157 AD) and makes him the Emperor. As such, the Emperor of Rome after Aurelius dies is NOT Commodus but Julius. Julius has a much better term as Emperor than Commodus. As a result, Rome lasts longer and when it collapses, it is split and reunited several times. In the modern day, Rome is under a single Emperor. What if this had happened what if the Mediterranean remained the Mare Nostrum?