|Centuries:||1st century – 2nd century – 3rd century|
|Decades:||90s 100s 110s – 120s – 130s 140s 150s|
|Years:||117 118 119 – 120 – 121 122 123|
|120 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||873|
|Bahá'í calendar||−1724 – −1723|
|English Regnal year||N/A|
|Chinese calendar||己未年 (Earth Goat)
2816 or 2756
— to —
庚申年 (Metal Monkey)
2817 or 2757
|Coptic calendar||−164 – −163|
|- Vikram Samvat||176–177|
|- Shaka Samvat||42–43|
|- Kali Yuga||3221–3222|
|Igbo calendar||−880 – −879|
|Iranian calendar||502 BP – 501 BP|
|Islamic calendar||517 BH – 516 BH|
|Minguo calendar||1792 before ROC
|Thai solar calendar||663|
|Wikimedia Commons has media related to 120.|
Year 120 (CXX) was a leap year starting on Sunday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Severus and Fulvus (or, less frequently, year 873 Ab urbe condita). The denomination 120 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.
- Emperor Hadrian visits Britain.
- Foss Dyke is constructed in Britain.
- An Indian ambassadorial contingent visits with Hadrian.
- Suetonius becomes Hadrian's secretary ab epistolis.
- Market Gate of Miletus, from Miletos, is built. (approximate date) It is now kept at Staatliche Museen zu Berlin, Preussischer Kulturbesitz, Antikensammlung.
- Change of era name from Yuanchu (7th year) to Yongning of the Chinese Eastern Han Dynasty.
- The Scythians dominate western India: Punjab, Sind, the north of Gujerat and a portion of central India.
- February 8 – Vettius Valens, Hellenistic astrologer (d. c. 175)
- Irenaeus, Christian bishop and apologist (d. 202)
- Lucian, Syrian rhetorician and satirist, writing in the Greek language (d. 180)
- Jesus of Nazareth (approx. date according to some Muslims, he is believed to have survived crucifixion and migrated towards the East where he died naturally of old age and is believed to be buried at the Roza Bal shrine in Srinagar, Kashmir) 
- Dio Chrysostom, Greek historian (approximate date) (b. c. 40)
- Nicomachus, Greek mathematician (approx. date) (b. 60)
- Sextus Pedius, Roman jurist (b. 50)
- Saint Matthias of Jerusalem, Bishop of Jerusalem
- Marcian of Tortona (or in 117), martyred saint
- Getulius, Saint Hermes, martyred saints