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.

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• February 8 – Vettius Valens, Greek astrologer (d. 175)
• Irenaeus, Greek bishop and apologist (approximate date)
• Lucian, Syrian rhetorician and satirist (approximate date)
• Tatian, Syrian Christian writer and theologian (d. 180)

• Ban Zhao, Chinese historian and philosopher (b. AD 49)
• Dio Chrysostom, Greek historian (approximate date)
• Faustinus and Jovita, Roman Christian martyrs
• Getulius, Roman officer and Christian martyr
• Hermes, Greek Christian martyr and saint
• Marcian of Tortona, Roman bishop (or 117)
• Matthias of Jerusalem, bishop of Jerusalem
• Nicomachus, Greek mathematician (b. AD 60)
• Plutarch, Greek philosopher (approximate date)
• Sextus Pedius, Roman jurist (b. AD 50)
• Tacitus, Roman historian^[1]