The retirement of the Bishop of Rome, the first in 600 or so years, reminds me of an old trivia question: Who was the first Roman Emperor to retire?
This emperor's retirement palace  in Split, Croatia remains in good condition after 1700 years, full of shops and restaurants. It was largely forgotten in Northern Europe, until British architect Robert Adam surveyed it in the 1760s.
Publication of Adam's book on this emperor's retirement palace had a major influence on the development of the craze for Neo-Classical architecture (e.g., Thomas Jefferson's design for the University of Virginia).
Answer under the fold:
Diocletian  in 305 A.D., due to a debilitating illness:
When begged to return to the throne a few years later, he replied:
"If you could show the cabbage that I planted with my own hands to your emperor, he definitely wouldn't dare suggest that I replace the peace and happiness of this place with the storms of a never-satisfied greed."
He died in 311.
In general, though, Roman Emperors (and Empresses) did not find retirement appealing. When the Blue and Green chariot racing fans had taken control of Constantinople in 532, the Emperor Justinian was about to flee in despair, when his Empress, the former "actress" Theodora, refused to give up her throne, saying "purple makes a fine shroud." Shaming the men, her courage inspired them to come up with a plan for dividing and conquering the sports hooligans, allowing the Byzantine Empire to survive another 1021 years.