Year 847 (DCCCXLVII) was a common year starting on Saturday of the Julian calendar.

• Danish Vikings land in the Breton March (western part of Gaul). Duke Nominoe of Brittany fails to withstand them in battle, but succeeds in buying them off with gifts and persuading them to leave (approximate date).
• Viking Age: The Vikings plunder the Lower Rhine, as part of their attacks on the Empire of Francia.
• The Saracens, under the Berber leader Kalfun, capture the Byzantine city of Bari (Southern Italy). He becomes the first ruler of the Emirate of Bari, and expands his influence on the Italian mainland with raids.^[1]

• August 10 – Caliph Al-Wathiq dies of dropsy after a five-year reign. He is succeeded by his brother al-Mutawakkil.

• November 24 – 847 Damascus earthquake

• January 24 – Pope Sergius II dies of gout after a 3-year reign. He is succeeded by Leo IV, as the 103rd pope of Rome.
• April 21– Rabanus Maurus, a Frankish Benedictine monk, becomes archbishop of Mainz after the death of Odgar.

• Æthelred I, king of Wessex (approximate date)
• Al-Mu'tazz, Muslim caliph (d. 869)
• Charles the Child, king of Aquitaine (or 848)
• Cheng Ji, Chinese general (approximate date)
• Fujiwara no Sukeyo, Japanese aristocrat (d. 897)
• Kang Junli, general of the Tang Dynasty (d. 894)
• Lu Yi, chancellor of the Tang Dynasty (d. 905)
• Miyoshi Kiyotsura, Japanese scholar (d. 918)
• Wang Jian, emperor of Former Shu (d. 918)
• Wang Jingchong, Chinese general (d. 883)

• January 27 – Sergius II, pope of the Catholic Church (b. 790)
• April 21 – Odgar, Frankish monk and archbishop
• June 1 – Xiao, empress of the Tang Dynasty
• June 14 – Methodius I, patriarch of Constantinople
• August 10 – Al-Wathiq, Muslim caliph (b. 816)
• Fedelmid mac Crimthainn, king of Munster (Ireland)
• Frothar of Toul, Frankish bishop (approximate date)
• Hetto, Frankish archbishop (approximate date)
• Isa ibn Mansur al-Rafi'i, Muslim governor
• Muhammad ibn al-Zayyat, Abbasid vizier
• Li Rangyi, chancellor of the Tang Dynasty
• Theodemar of Iria, Galician bishop

• Kennedy, Hugh (2006). When Baghdad Ruled the Muslim World: The Rise and Fall of Islam's Greatest Dynasty. Cambridge, MA: Da Capo Press. ISBN 978-0-306814808.