Who was the longest-reigning Pope?
Pope Pius IX, the longest-reigning modern pope. Although the average reign of the pope from the Middle Ages was a decade, a number of those whose reign lengths can be determined from contemporary historical data are the following:
Pius IX (1846–1878): 31 years, 7 months and 23 days (11,560 days).
Leo XIII (1878–1903): 25 years, 5 months and 1 day (9,281 days).
Pius VI (1775–1799): 24 years, 6 months and 15 days (8,962 days).
Adrian I (772–795): 23 years, 10 months and 25 days (8,729 days).
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