|817 by topic|
|Ab urbe condita||1570|
|Balinese saka calendar||738–739|
|Chinese calendar||丙申年 (Fire Monkey)|
3513 or 3453
— to —
丁酉年 (Fire Rooster)
3514 or 3454
|- Vikram Samvat||873–874|
|- Shaka Samvat||738–739|
|- Kali Yuga||3917–3918|
|Japanese calendar||Kōnin 8|
|Minguo calendar||1095 before ROC|
|Seleucid era||1128/1129 AG|
|Thai solar calendar||1359–1360|
943 or 562 or −210
— to —
944 or 563 or −209
Year 817 (DCCCXVII) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar.
- Summer – Emperor Louis I issues an Ordinatio Imperii, an imperial decree that lays out plans for an orderly succession. He divides the Frankish Empire among his three sons: Lothair, the eldest, is proclaimed co-emperor in Aachen, and becomes the overlord of his brothers. He receives the dominion of Burgundy (including German and Gallic parts). Pepin, the second son, is proclaimed king of Aquitaine, and receives Gascony (including the marche around Toulouse and parts of Septimania); Louis (the youngest son) is proclaimed king of Bavaria, and receives the dominions of East Francia.
- Prince Grimoald IV is assassinated by a complot of Lombard nobles vying for his throne. He is succeeded by Sico as ruler of Benevento (Southern Italy), who is forced to pay an annual tribute of 7,000 solidi to Louis I.
- Ziyadat Allah I becomes the third Aghlabid emir of Ifriqiya (modern Tunisia). During his rule, the relationship between the Aghlabid Dynasty and the Arab troops remains strained.
- January 24 – Pope Stephen IV dies at Rome after a 7-month reign, and is succeeded by Paschal I as the 98th pope of the Catholic Church.
- Synod of Aachen: The council adopts a capitulare monasticum, containing the Benedictine rules of monastic life in the Frankish realm.
- Abu Dawud, Muslim hadith compiler (or 818)
- Al-Fath ibn Khaqan, Muslim governor (or 818)
- Pepin, count of Vermandois (approximate date)
- Pyinbya, king of Burma (d. 876)
- January 24 – Stephen IV, pope of the Catholic Church
- Grimoald IV, Lombard prince of Benevento
- Quriaqos of Tagrit, patriarch of Antioch
- Tibraide mac Cethernach, abbot of Clonfert
- Theophanes the Confessor, Byzantine monk (or 818)
- Wu Yuanji, general of the Tang Dynasty
- ^ Wickham, p. 154. In 818 according to the Annales Beneventani.