864

Year 864 (DCCCLXIV) was a leap year starting on Saturday (link will display the full calendar) of the Julian calendar.

Europe

 * Spring – Emperor Louis II (the Younger) 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 (Ireland). 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 (identified, although not unanimously, with Devín Castle in Slovakia).
 * 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 (Japan).
 * Hasan ibn Zayd establishes the Zaydid Dynasty, and is recognized as ruler of Tabaristan (Northern Iran).

Religion

 * The Christianization of Bulgaria begins: Boris I, ruler (Knyaz) of the Bulgarian Empire, is converted to Orthodox Christianity. His family and high-ranking dignitaries accept the Orthodox faith at the capital, Pliska - from this point onwards the rulers of the Bulgarian Empire are known as ‘Tsars’ rather than ‘Khans’.

Births

 * Gu Quanwu, general of the Tang Dynasty (d. 931)
 * Khumarawayh ibn Ahmad ibn Tulun, ruler of the Tulunid Dynasty (d. 896)
 * Louis III, king of the West Frankish Kingdom (or 863)
 * Muhammad ibn Ya'qub al-Kulayni, Muslim scholar (d. 941)
 * Simeon I, ruler (tsar) of the Bulgarian Empire (or 865)
 * Yúnmén Wényǎn, Chinese Zen master (or 862)

Deaths

 * September 13 – Pietro Tradonico, doge of Venice
 * Al-Fadl ibn Marwan, Muslim vizier
 * Al-Fadl ibn Qarin al-Tabari, Muslim governor
 * Arnold of Gascony, Frankish nobleman
 * Bi Xian, chancellor of the Tang Dynasty (b. 802)
 * Ennin, Japanese priest and traveler
 * Hucbert, Frankish nobleman (b. 820)
 * Laura, Spanish abbess
 * Lorcán mac Cathail, king of Uisneach (Ireland)
 * Muhammad ibn al-Fadl al-Jarjara'i, Muslim vizier (or 865)
 * Pei Xiu, chancellor of the Tang Dynasty (b. 791)
 * Sancho II, count of Gascony (approximate date)
 * Sergius I, duke of Naples
 * Trpimir I, duke (knez) of Croatia
 * Yahya ibn Umar, Muslim imam (or 865)