|Covid-19|Prince Sicard of Benevento is assassinated by a conspiracy among the nobility. He is succeeded by Radelchis I, chief army officer and treasurer of Sicard, who proclaims himself ruler of Benevento. He imprisons Siconulf, heir and brother of Sicard, in Taranto. But Amalfitan merchants, led by Landulf I, the gastald of Capua, and with the support of Guaifer, rescue him from prison. Siconulf is proclaimed prince of Salerno, and a civil war erupts, which splits the Lombard principality in Southern Italy.
Third Civil War: King Louis the German, grandson of Charlemagne, invades Swabia. His nephew, Pepin II of Aquitaine, and his Gascon subjects, conquer territory all the way to the Loire.
Approximate date – Danish Vikings return to ravage the Frisian coast (sacking Dorestad for the second time).
King Egbert of Wessex dies after a 37-year reign, and is succeeded by his son Æthelwulf ("Noble Wolf") as ruler of Wessex. Æthelwulf's eldest son, Æthelstan, is made sub-king of Kent, Essex, Surrey and Sussex, under his father.
Approximate date – Alpín II begins his reign as king of Dál Riata (modern Scotland).
Charles the Fat, Frankish emperor (d. 888)
He Quanhao, general of the Tang Dynasty (d. 870)
Liu Chongwang, chancellor of the Tang Dynasty (d. 900)
Muhammad ibn Jarir al-Tabari, Persian scholar (d. 923)
Áed mac Boanta, king of Dál Riata
Aznar I, king of Aragon
Cathal mac Muirgiussa, king of Connacht
Chengguan, Chinese Buddhist monk (b. 738)
Cummascach mac Congalaig, king of Brega
Egbert, king of Wessex
Eóganan mac Óengusa, king of the Picts
Ibrahim ibn al-Mahdi, Muslim prince (b. 779)
Muhammad at-Taqi, Muslim ninth Ismā'īlī imam (or 840)
Muiredach mac Eochada, king of Ulaid
Pei Du, chancellor of the Tang Dynasty (b. 765)
Rorgon I, count of Maine (or 840)
Sicard, prince of Benevento
Vache, prince of Kakheti
Wiglaf, king of Mercia
Year 839 (DCCCXXXIX) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar.