New Rome, new home
I believe that Maximinus Thrax, whose brief reign ran from 235 to 238 AD, was the first Roman emperor never to have set foot in Rome. The Thracian brute started a trend. As the years went by, more and more Roman emperors gave the city a miss. Diocletian (284-305), who brought the crisis of the third century to an end, hated the city. Some later emperors settled on Ravenna as the seat of power for the Western empire. Constantinople emerged as HQ for the East. Rome retained a certain ceremonial significance but was increasingly irrelevant to the business of empire. The turn away from Rome happened for many reasons.