This a chart showing the reigns and lifespans of the greatest Byzantine Emperors.
As you can clearly see, most of the emperors who tended to have long reigns had lifespans which provided stability to the Eastern Romans. Emperor Anastasius I whose reign covers the 5th and early 6th Centuries had the longest lifespan on this chart while Constantine V had the shortest lifespan.
The ability for the Byzantine Empire to have multiple Emperors with long lifespans one after another helped to keep the empire on a steady footing in the chaotic Middle Ages.
Byzantine-Empire.com 