Year 798 (DCCXCVIII) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. The denomination 798 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
|Ab urbe condita||1551|
|Balinese saka calendar||719–720|
|Chinese calendar||丁丑年 (Fire Ox)|
3494 or 3434
— to —
戊寅年 (Earth Tiger)
3495 or 3435
|- Vikram Samvat||854–855|
|- Shaka Samvat||719–720|
|- Kali Yuga||3898–3899|
|Japanese calendar||Enryaku 17|
|Minguo calendar||1114 before ROC|
|Seleucid era||1109/1110 AG|
|Thai solar calendar||1340–1341|
924 or 543 or −229
— to —
925 or 544 or −228
- Battle of Bornhöved: King Charlemagne forms an alliance with the Obodrites. Together with Prince Drożko (Thrasco), he defeats the Nordalbian Saxons near the village of Bornhöved (modern-day Neumünster), obliging these 'northerners' to submit and give hostages against their future good behavior. In the coming years they are granted areas of present-day Hamburg.
- King Charles the Younger, a son of Charlemagne, conquers Corsica and Sardinia (approximate date).
- King Coenwulf of Mercia invades Gwynedd (modern Wales), and kills his rival Caradog ap Meirion during the fighting in Snowdonia. Kings Cynan and Hywel retake the throne. Coenwulf also defeats and captures King Eadberht Præn of Kent. He is blinded and his hands are cut off. He introduces his brother Cuthred as a sub-king of Kent (approximate date).
- Battle of Billington: King Eardwulf of Northumbria defeats the nobleman Wada in battle, who has killed former King Æthelred I (see 796).
- King Sigeric I of Essex abdicates and departs for a pilgrimage to Rome. He is succeeded by his son Sigered.
- King Alfonso II of Asturias campaigns against the Arab Muslims in Al-Andalus. With Frankish military support, he raids into Andalusia and sacks Lisbon (modern Portugal).
- Bahlul ibn Marzuq, a Vascon-Muslim military leader, revolts in Zaragoza against the Arab-Muslim government of Al-Andalus.
- Alcuin, Anglo-Saxon monk and scholar, writes to his friend, the exiled king Osbald of Northumbria, in order to dissuade him.
- Theodulf, Frankish poet, is appointed bishop of Orléans. He becomes one of Charlemagne's favoured theologians.
- David Nicolle (2014). The Conquest of Saxony AD 782–785, p. 82. ISBN 978-1-78200-825-5.
- The Anglo-Saxon Chronicle, manuscript E, year 796 (798). Translation by Michael Swanton, 1996.
- Picard, Christophe (2000). Le Portugal musulman (VIIIe-XIIIe siècle0. L'Occident d'al-Andalus sous domination islamique. Paris: Maisonneuve & Larose. p. 109. ISBN 2-7068-1398-9.