Pius IX, for example, holds the record for the longest verified papal reign, which lasted 11,560 days. The Gregorian calendar, still in use today, was introduced by Pope Gregory XIII in 1582.

Of those popes, Francis had the ninth-longest papacy.Over the past 200 years, the longest papacy was that of Pope Pius IX, who served over ... they take on a new papal name that replaces their ...