840

840 in various
AG
Thai solar calendar	1382–1383
Tibetan calendar	阴土羊年; (female Earth-Goat); 966 or 585 or −187; — to —; 阳金猴年; (male Iron-Monkey); 967 or 586 or −186

Millennium:	1st millennium
Centuries:	8th century; 9th century ; 10th century;
Decades:	820s; 830s; 840s ; 850s; 860s;
Years:	837; 838; 839; 840 ; 841; 842; 843;

Year 840 (DCCCXL) was a leap year starting on Thursday in the Julian calendar, the 840th year of the Common Era (CE) and Anno Domini (AD) designations, the 840th year of the 1st millennium, the 40th year of the 9th century, and the 1st year of the 840s decade.

Events

imperial palace at Ingelheim, while suppressing a revolt. His eldest son Lothair I succeeds him as Holy Roman Emperor, and tries to seize all the territories of the late Charlemagne. Charles the Bald, 17, becomes king of the Franks, and joins with his half-brother Louis the German
, in resisting Lothair.

King Wigstan of Mercia, grandson of former ruler Wiglaf (see 839), declines his kingship in preference of the religious life. He asks his widowed mother, Princess Ælfflæd, to act as regent. A nobleman of the line of the late king Beornred, named Berhtric, wishes to marry her but he is a relative. Wigstan refuses the match, and is murdered by followers of Berhtric at Wistow. He is buried at Repton Abbey, and later revered as a saint. The Mercian throne is seized by Berhtric's father, Beorhtwulf.^[1]^{: 238–239}
Vikings make permanent settlements with their first 'wintering over', located at Lough Neagh in Northern Ireland (approximate date).

Emperor Wenzong (Li Ang) dies after a 13-year reign, in which he has failed to break the power of his palace eunuchs. He is succeeded by his brother Wu Zong, as Chinese ruler of the Tang dynasty.
The
Yenisei River, and sack with a force of around 80,000 horsemen the Uyghur capital, Ordu-Baliq (driving the Uyghurs out of Mongolia). This ends the Uyghur Khaganate.^[2]

The 840 Erzurum earthquake takes place in the city of Qaliqala (modern Erzurum).^[3]

January – Michael III, Byzantine emperor (d. 867) This date of birth is generally held as uncertain; though January 840 is the most probable, 839 is also possible.
October 25 – Ya'qub ibn al-Layth al-Saffar, founder of the Saffarid dynasty (d. 879)
Abu al-Hassan al-Nuri, Muslim Sufi
(approximate date)

Millennium:	1st millennium
Centuries:	8th century 9th century 10th century
Decades:	820s 830s 840s 850s 860s
Years:	837 838 839 840 841 842 843