Let's suppose that Roman Emperor Theodosius I, had a third son named Liberius.
So, after his death in 395 A.D. the Empire splits in three.
Arcadius takes the East as in OTL, Honorius takes the West with Cenabum as capital, and Liberius takes the middle one hailing from Ravenna..
How things play out? Is the Middle Empire more viable than OTL WRE?