Hosta

Year 804 (DCCCIV) was a leap year starting on Monday (link will display the full calendar) of the Julian calendar.

Events

Battle of Krasos: Emperor Nikephoros I refuses to pay the tribute imposed by Caliph Harun al-Rashid of the Abbasid Caliphate. A Muslim-Arab expeditionary force invades Asia Minor. During a surprise attack, Nikephoros suffers a major defeat against the Saracens at Krasos in Phrygia. According to Arabian sources, the Byzantines lose 40,700 men and 4,000 pack animals, while Nikephoros himself is almost killed, but saved by the bravery of his officers.^[1]^[2]
Abbasid caliph Harun al-Rashid marries Abbasa, the daughter of Abbasid prince and official Sulayman.

Summer – Emperor Charlemagne finishes the conquest of Saxony. The Carolingian administration in the north is restored and the diocese of Bremen is re-established.^[3] Venice, torn by infighting, switches allegiance from Constantinople to King Pepin of Italy, son of Charlemagne.
Obelerio degli Antenori becomes the ninth doge of Venice, after his predecessor Giovanni Galbaio flees to Mantua, where he is killed.
The Gymnasium Carolinum in Osnabrück is founded by Charlemagne (the oldest school in Germany).^[4]

Kūkai, Japanese Buddhist monk, travels in a government-sponsored expedition to China, in order to learn more about the Mahavairocana Sutra. He brings back texts of Shingon (Esoteric Buddhism).
Priest Saichō, patriarch of Tendai Buddhism, visits China and reportedly brings back tea seeds (or 805).
The Inscription of Sukabumi from Eastern Java marks the beginning of the Javanese language.

Ludger, Frisian missionary, becomes the first bishop of Münster, and builds a monastery there.

Bosworth, C. E., ed. (1989). The History of al-Ṭabarī, Volume XXX: The ʿAbbāsid Caliphate in Equilibrium: The Caliphates of Mūsā al-Hādī and Hārūn al-Rashīd, A.D. 785–809/A.H. 169–192. SUNY Series in Near Eastern Studies. Albany, New York: State University of New York Press. ISBN 978-0-88706-564-4.
Mango, Cyril; Scott, Roger (1997). The Chronicle of Theophanes Confessor. Byzantine and Near Eastern History, AD 284–813. Oxford University Press. ISBN 0-19-822568-7.
Nicolle, David (2014). The Conquest of Saxony AD 782–785. ISBN 978-1-78200-825-5.
Treadgold, Warren (1988). The Byzantine Revival, 780–842. Stanford, California: Stanford University Press. ISBN 978-0-8047-1462-4.