|Covid-19|June 14 – Euphemius, exiled Byzantine admiral, asks for the help of North African Arabs, to retake Sicily and Malta from the Byzantines. Emir Ziyadat Allah I of Ifriqiya promises to return the islands to Euphemius, in exchange for a yearly tribute, and sends an Arab Muslim expeditionary force of 10,000 men under the 70-year-old Asad ibn al-Furat, which lands at Mazara del Vallo in Sicily.
Fall – Siege of Syracuse: Muslim forces under Asad ibn al-Furat, in support of the rebel Byzantine army, besiege Syracuse, Sicily.
Summer – Omurtag, ruler (khan) of the Bulgarian Empire, launches an attack to the West, and penetrates into Pannonia. He expels the local chiefs, and installs Bulgar governors over the Slavic tribes to control them. Omurtag conquers the cities of Beograd, Braničevo, Sirmium, and most of eastern Slavonia.
Giustiniano Participazio deposes his younger brother Giovanni I, and is appointed doge of Venice. Giovanni, who is part of a pro-Frankish faction, is exiled to Zara (modern Croatia).
Æthelstan establishes himself as king of East Anglia, after killing King Ludeca of Mercia in battle. Ludeca is succeeded by Wiglaf, father-in-law (and probably distant cousin) of the late king Ceolwulf I's daughter.
Emperor Jing Zong is assassinated by a group of conspirators. He is succeeded by his brother Wen Zong, as ruler of the Tang Dynasty.
August 27 – Pope Eugene II dies after a 3-year reign, and is succeeded by Valentine as the 100th pope of the Catholic Church.
October 10 – Pope Valentine dies just after a two-month reign, and is succeeded by Gregory IV as the 101st pope of Rome.
Chalid Ben Abdulmelik and Ali Ben Isa travel to the Plain of Sinjar (modern Iraq), under orders of Caliph Al-Ma'mun, to measure the size of the Earth.
The Saracens, who found spinach originally in Persia (modern Iran), introduce the plant to Sicily.
Ali ibn Muhammad, Muslim sultan (d. 848)
Cyril, Byzantine missionary and bishop (d. 869)
Ibn al-Rawandi, Muslim scholar and writer (d. 911)
January 1 – Adalard of Corbie, Frankish abbot
August 27 – Eugene II, pope of the Catholic Church
October 10 – Valentine, pope of the Catholic Church
Agnello Participazio, doge of Venice
Claudius, archbishop of Turin
Grigol of Kakheti, Georgian prince
Guillemundus, Frankish nobleman
Hildegrim, bishop of Châlons
Jing Zong, emperor of the Tang Dynasty (b. 809)
Li Yi, Chinese poet (or 829)
Ludeca, king of Mercia
Wu Chongyin, Chinese general (b. 761)
Yaoshan Weiyan, Chinese Buddhist monk (b. 745)
Year 827 (DCCCXXVII) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar.