|Millennium:||1st millennium BC|
|120 BC by topic|
|Gregorian calendar||120 BC|
|Ab urbe condita||634|
|Ancient Egypt era||XXXIII dynasty, 204|
|- Pharaoh||Ptolemy VIII Physcon, 26|
|Ancient Greek era||165th Olympiad (victor)¹|
|Balinese saka calendar||N/A|
|Chinese calendar||庚申年 (Metal Monkey)|
2577 or 2517
— to —
辛酉年 (Metal Rooster)
2578 or 2518
|Coptic calendar||−403 – −402|
|Ethiopian calendar||−127 – −126|
|- Vikram Samvat||−63 – −62|
|- Shaka Samvat||N/A|
|- Kali Yuga||2981–2982|
|Iranian calendar||741 BP – 740 BP|
|Islamic calendar||764 BH – 763 BH|
|Minguo calendar||2031 before ROC|
|Seleucid era||192/193 AG|
|Thai solar calendar||423–424|
7 or −374 or −1146
— to —
8 or −373 or −1145
Year 120 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Manilius and Carbo (or, less frequently, year 634 Ab urbe condita) and the Third Year of Yuanshou. The denomination 120 BC 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.
Beginning of the kingdom Osroene. The end of the kingdom is in 244 AD.
- The Teutons and the Cimbri migrate south and west to the Danube valley where they encounter the expanding Roman Republic (approximate date).
- Retaliating against the Han conquest of the Hexi Corridor in the previous year, the Xiongnu invade the provinces of Youbeiping and Dingxiang, killing or capturing over 1000 inhabitants.
- May 21 – Aurelia Cotta, mother of Julius Caesar (d. 54 BC)
- Berenice III, reigning Queen of Egypt (d. 80 BC)
- Lucius Cornelius Sisenna, writer and politician (d. 67 BC)
- Verres, corrupt praetor (approximate date) (d. 43 BC)
- Hipparchus, Greek astronomer and mathematician, on Rhodes (approximate date) (b. c. 190 BC)
- ^ Qian, Sima. Records of the Grand Historian, Section: Xiongnu, Section: Wei Qing & Huo Qubing.