819

By place

Europe

• Spring - Emperor Louis I marries Judith of Bavaria in Aachen. She becomes his second wife and Empress of the Franks. Like many of the royal marriages of the time, Judith is selected through a bridal show.
• Ljudevit, duke of Pannonian Croatia, allies himself with the Slavs and raises a rebellion against the Frankish Empire. Louis I sends an army led by Cadolah of Friuli, but is defeated by the Pannonian Slavs.
• Battle of Kupa: Ljudevit defeats the Frankish forces led by Borna, a vassal of Louis I. He escapes with the help of his elite bodyguard. Ljudevit uses the momentum and invades the Duchy of Croatia.
• Nominoe, a noble Briton, is appointed by Louis I as count of Vannes in Brittany.

  Abbasid Caliphate

• August 11 - Caliph Al-Ma'mun returns to Baghdad, securing the city's place as the capital of the Abbasid Caliphate.