Three popes were deposed in one day by Holy Roman Emperor Henry III today in 1047. Rebels had replaced Pope Benedict IX; Benedict had deposed his replacement, and then, for a massive bribe (marital as well as financial) stepped down in favour of a third contender. Later, Benedict’s family had decided he wanted the job back. Henry did the decent thing and got rid of them all, appointing a reforming pope, Leo IX.
Pope Pius XI issued the encyclical Ad Catholici Sacerdotii today in 1935, advising priests on how to do the job better.