340s
The 340s decade ran from January 1, 340, to December 31, 349.
| Millennium: | 1st millennium |
| Centuries: | 3rd century – 4th century – 5th century |
| Decades: | 310s 320s 330s – 340s – 350s 360s 370s |
| Years: | 340 341 342 343 344 345 346 347 348 349 |
| Categories: | Births – Deaths – Architecture Establishments – Disestablishments |
Events
Significant people
- Constans, Roman Emperor
- Constantius II, Roman Emperor
- Flavius Philippus, praetorian prefect of the East, consul
- Hypatia of Alexandria