864

By place

Europe

• Spring - Emperor Louis II marches with a Frankish army against Rome. While en route to the papal city, he becomes ill, and decides to make peace with Pope Nicholas I.
• July 25 - Edict of Pistres: King Charles the Bald orders defensive measures against the Vikings. He creates a large force of cavalry, which inspires the beginning of French chivalry.
• Viking raiders, led by Olaf the White, arrive in Scotland from the Viking settlement of Dublin. He rampages the country, until his defeat in battle by king Constantine I.
• Robert the Strong, margrave of Neustria, attacks the Loire Vikings in a successful campaign. Other Viking raiders plunder the cities of Limoges and Clermont, in Aquitaine.
• King Louis the German invades Moravia, crossing the Danube River to besiege the civitas Dowina.
• Pepin II joins the Vikings in an attack on Toulouse. He is captured while besieging the Frankish city. Pepin is deposed as king of Aquitaine, and imprisoned in Senlis.
• September 13 - Pietro Tradonico dies after a 28-year reign. He is succeeded by Orso I Participazio, who becomes doge of Venice.
• King Alfonso III conquers Porto from the Emirate of Cordoba. This is the end of the direct Muslim domination of the Douro region.

  Asia

• Mount Fuji, located on Honshu Island, erupts for 10 days, in an event known as the Jōgan eruption.
• Hasan ibn Zayd establishes the Zaydid Dynasty, and is recognized as ruler of Tabaristan.

  By topic

Religion

• The Christianization of Bulgaria begins: Boris I, ruler of the Bulgarian Empire, is converted to Orthodox Christianity. His family and high-ranking dignitaries accept the Orthodox faith at the capital, Pliska.