Year 342 (CCCXLII) was a common year starting on Friday (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 Claudius (or, less frequently, year 1095 Ab urbe condita). The denomination 342 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||1095|
|Balinese saka calendar||263–264|
|Chinese calendar||辛丑年 (Metal Ox)|
3038 or 2978
— to —
壬寅年 (Water Tiger)
3039 or 2979
|- Vikram Samvat||398–399|
|- Shaka Samvat||263–264|
|- Kali Yuga||3442–3443|
|Iranian calendar||280 BP – 279 BP|
|Islamic calendar||289 BH – 288 BH|
|Minguo calendar||1570 before ROC|
|Seleucid era||653/654 AG|
|Thai solar calendar||884–885|
468 or 87 or −685
— to —
469 or 88 or −684
- The Western Roman Emperor Constans campaigns in Britain against the Picts.
- Constans campaigns victoriously against the Franks.
- The Senate abolishes gay marriage.
- A large earthquake strikes Cyprus.
- Goguryeo is invaded by Murong Huang of the Xianbei.
- Jin Kangdi succeeds his brother Jin Chengdi as emperor of China.
- Paul I, Patriarch of Constantinople, is deposed and replaced by Macedonius I.
- February 15 – The original Hagia Sophia is dedicated in Constantinople.