Year 123 (CXXIII) was a common year starting on Thursday of the Julian calendar. At the time, it was known as the Year of the Consulship of Paetinus and Apronius (or, less frequently, year 876 Ab urbe condita). The denomination 123 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 averts a war with Parthia by a personal meeting with Osroes I (according to the Historia Augusta, disputed).^[1]
• Housesteads Fort is constructed on Hadrian's Wall north of Bardon Mill.
• Hadrian's Villa at Tivoli is built.
• The Temple of Al-Lat in Palmyra is dedicated somewhere between this year and 164 AD.

• In China, Ban Yong, son of Ban Chao, reestablishes the Chinese control over the Tarim Basin.
• The Chinese government establishes Aide of the Western Regions over the Tarim Basin.

• Hadrian leads a punitive campaign against Berbers who had been raiding Roman towns in Roman Mauretania.^[2]

• Chinese scientist Zhang Heng corrects the calendar to bring it into line with the four seasons.

• Annia Cornificia Faustina, sister of Marcus Aurelius (d. 158)