Pope Sergius II was Pope from January 844 to his death in 847.
Born of a noble family, Sergius was educated in the schola cantorum, was ordained Cardinal-priest of the Church of Sts. Martin and Sylvester by Pope Paschal. Under Gregory IV, he became archpriest.
At a preliminary meeting to designate a successor to Gregory, the name of Sergius was nominated by the aristocracy, while the people of Rome declared for the deacon John. The opposition was suppressed, with Sergius intervening to save John's life. John was, however, shut up in a monastery, and Sergius was duly consecrated, without seeking ratification of the Frankish court.
The Holy Roman Emperor Lothair I, however, disapproved of this abandonment of the Constitutio Romana of 824, which included a statute that no pope should be consecrated until his election had the approval of the Frankish emperor. He sent an army under his son Louis, the recently appointed Viceroy of Italy, to re-establish his authority. The Church and the Emperor reached an accommodation, with Sergius crowning Louis King of Lombardy, although the Pope did not accede to all the demands made upon him.
Sergius contributed to urban redevelopment in Rome, improving churches, aqueducts, and the Lateran Basilica. He and his brother, Benedict, funded their building plans by selling appointments to various church positions to the highest bidder.
During his pontificate the outskirts of Rome were ravaged, and the churches of St. Peter and St. Paul were sacked by Arabs, who also approached Portus and Ostia in August 846. During the raid, he (along with the people of Rome) looked on helplessly as they hid behind the Aurelian walls. Despite having been forewarned of the intentions of the raiders, Sergius is seen as having not acted adequately enough to prepare for that which eventuated.
Sergius died while negotiating between two patriarchs and was succeeded by Pope Leo IV.