|Centuries:||3rd century – 4th century – 5th century|
|Decades:||320s 330s 340s – 350s – 360s 370s 380s|
|Years:||354 355 356 – 357 – 358 359 360|
|357 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1110|
|Chinese calendar||丙辰年 (Fire Dragon)
3053 or 2993
— to —
丁巳年 (Fire Snake)
3054 or 2994
|- Vikram Samvat||413–414|
|- Shaka Samvat||279–280|
|- Kali Yuga||3458–3459|
|Iranian calendar||265 BP – 264 BP|
|Islamic calendar||273 BH – 272 BH|
|Minguo calendar||1555 before ROC
|Seleucid era||668/669 AG|
|Thai solar calendar||899–900|
Year 357 (CCCLVII) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Iulianus (or, less frequently, year 1110 Ab urbe condita). The denomination 357 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.
- April 28 – Emperor Constantius II enters Rome for the first time to celebrate his victory over Magnentius. He address the Senate and the Roman people.
- August 25 – Battle of Strasbourg: Julian, Caesar (deputy emperor) and supreme commander of the Roman army in Gaul, wins an important victory against the Alemanni at Strasbourg (Argentoratum), driving the barbarians back behind the Rhine.
- Julian builds in Gaul a fleet to secure the corn supply from Britain, for the garrisons (castella) of the Rhine.
- The Imperial Library of Constantinople is founded.
- Ammianus Marcellinus describes the Pantheon as being "rounded like the boundary of the horizon and vaulted with a beautiful loftiness".
- Winter – Constantius II receives ambassadors from the Persian Empire. They demand that Rome restore the lands surrendered by King Narseh.
- The reign of Fú Jiān, the emperor of Former Qin, commences in China.
- The Alans rout the Hun army in Western Asia.
- Saran, King of Ulster, is overthrown.
- Late in the year Pope Liberius travels to Sirmium (Pannonia) and agrees to sign documents that effectively undo the Nicene Creed (which has implicitly disavowed Arianism) and to sever his relationship with the former Alexandrian patriarch Athanasius, who is replaced as bishop of Alexandria by his Arian opponent George of Cappadocia.
- At about this date, the relics of St Andrew the Apostle are taken from Patras to Constantinople by order of the Emperor Constantius II, and deposited in the Church of the Holy Apostles.
- According to Jerome.