|Millennium:||1st millennium BC|
|123 BC by topic|
Year 123 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Balearicus and Flamininus (or, less frequently, year 631 Ab urbe condita). The denomination 123 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.
- Gaius Gracchus elected Roman tribune for the first time. He waited until after his re-election the following year before pushing forward the various civil and agrarian reforms that his brother championed in 133 BC.
- Aix-en-Provence founded under the name of Aquae Sextiae by the Roman consul Sextius Calvinus.
- Quintus Caecilius Metellus conquers the Balearic Islands for Rome, for which he earns the cognomen "Balearicus." He settles 3,000 Roman and Iberian colonists on the islands and founds the cities of Palma and Pollentia.