|Millennium:||1st millennium BC|
|51 BC by topic|
|Wikimedia Commons has media related to 51 BC.|
Year 51 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Marcellus and Sulpicius (or, less frequently, year 703 Ab urbe condita). The denomination 51 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.
- Consuls: Marcus Claudius Marcellus and Servius Sulpicius Rufus.
- Pompey demands that Julius Caesar lay down his command before he can stand for consul.
- Spring – Pharaoh Ptolemy XII dies and is succeeded by his eldest surviving daughter Cleopatra VII and her younger brother and co-ruler Ptolemy XIII.
- Publius Sulpicius Quirinius, Roman governor of Syria (d. 21 AD)
- Cheng, Emperor of the Han Dynasty of China (d. 7 BC)
- Spring – Pharaoh Ptolemy XII of Egypt (b. 117 BC)
- Posidonius of Apamea, Greek philosopher, astronomer, geographer (b. c. 135 BC)