|Centuries:||7th century – 8th century – 9th century|
|Decades:||690s 700s 710s – 720s – 730s 740s 750s|
|Years:||718 719 720 – 721 – 722 723 724|
|721 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1474|
|Bahá'í calendar||−1123 – −1122|
|English Regnal year||N/A|
|Chinese calendar||庚申年 (Metal Monkey)
3417 or 3357
— to —
辛酉年 (Metal Rooster)
3418 or 3358
|- Vikram Samvat||777–778|
|- Shaka Samvat||643–644|
|- Kali Yuga||3822–3823|
|Igbo calendar||−279 – −278|
|Japanese calendar||Yōrō 5
|Minguo calendar||1191 before ROC
|Thai solar calendar||1264|
|Wikimedia Commons has media related to 721.|
Year 721 (DCCXXI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. The denomination 721 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.
- February 13 – Theuderic IV succeeds Chilperic II as Merovingian King of the Franks, under the control of the Mayor of the Palace, Charles Martel.
- June 9 – Battle of Toulouse: after besieging Toulouse for three months, Al-Samh ibn Malik al-Khawlani, the Wāli (governor) of Al-Andalus (Muslim Spain), is defeated (and dies of his injuries) by Odo the Great, Duke of Aquitaine, preventing the spread of Umayyad control westward from Narbonne into Aquitaine.
- Anbasa ibn Suhaym Al-Kalbi is appointed governor of Al-Andalus.
- Prague is founded (according to legend) by the Princess Libuše and her husband Přemysl, founder of the eponymous dynasty.
- Rains and heavy storms around the southern seaport of Yangzhou destroy over 1,000 ships and boats in the usual congested waterway traffic of the Tang Dynasty.
- Abu Musa Jabir Ibn Hayyan (a.k.a. Geber), Arabian alchemist (approximate date)
- Al-Saffah, first Abbasid caliph (d. 754)
- Anastasius II, Byzantine Emperor
- Eadfrith, Bishop of Lindisfarne (698–721) and presumed author of the Lindisfarne Gospels
- Yao Chong, Chinese chancellor of the Tang Dynasty (born 650)
- Liu Zhiji, Chinese historian (born 661)
- Al-Samh ibn Malik al-Khawlani, the Arab governor general of Muslim Spain.
- 715, 718 or 721 – Khan Tervel of Bulgaria (b. c.675)