Year 674 (DCLXXIV) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. The denomination 674 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||1427|
|Balinese saka calendar||595–596|
|Chinese calendar||癸酉年 (Water Rooster)|
3370 or 3310
— to —
甲戌年 (Wood Dog)
3371 or 3311
|- Vikram Samvat||730–731|
|- Shaka Samvat||595–596|
|- Kali Yuga||3774–3775|
|Minguo calendar||1238 before ROC|
|Seleucid era||985/986 AG|
|Thai solar calendar||1216–1217|
800 or 419 or −353
— to —
801 or 420 or −352
- Siege of Constantinople: The Arab fleet enters the Sea of Marmara and appears before the southern walls of Constantinople, in an attempt to blockade the Byzantine capital.
- April – A Muslim expeditionary force disembarks on the Thracian shore (near Hebdomon), and lays siege to the massive Theodosian Walls, on the landward side to the west.
- Summer – Abu Ayyub al-Ansari, companion and standard-bearer of Muhammad, is killed during the first attempt of the siege of the city (approximate date).
- Winter – Arab forces under Yazid (son of caliph Muawiyah I) retire to Cyzicus (Turkey). For the next 4 years the Arab fleet installs a loose blockade around Constantinople.
- King Ecgfrith of Northumbria defeats a coalition led by the Mercians. He annexes the region of Lindsey (Lincolnshire).
- King Æscwine succeeds his father Cenfus as ruler of Wessex (approximate date).
- King Vikramaditya I of Chalukya defeats the Pallavan army in battle, and destroys its capital Kanchi (modern India).
- In Korea, Anapji is constructed by order of King Munmu of Silla.
- In Japan, Princess Ōku proceeds to the Ise Jingu.