Years: 823 824 825 826 - 827 - 828 829 830 831

Decades: 790s 800s 810s - 820s - 830s 840s 850s

Centuries: 8th century - 9th century - 10th century

Events

• Succession of Pope Valentine, then Pope Gregory IV.
• Arabs invade Sicily.
• The royal ceremonial centre at Copán is abandoned.
• Chalid Ben Abdulmelik and Ali Ben Isa measure the size of the Earth.

Births

• Saint Cyril, scholar, theologian, and linguist (d. 869)
• Emperor Montoku of Japan (d. 858)

Deaths

• Pope Eugene II
• September: Pope Valentine