| Millennium: | 1st millennium BC |
|---|---|
| Centuries: | 2nd century BC – 1st century BC – 1st century |
| Decades: | 80s BC 70s BC 60s BC – 50s BC – 40s BC 30s BC 20s BC |
| Years: | 54 BC 53 BC 52 BC – 51 BC – 50 BC 49 BC 48 BC |
| 51 BC by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishments and disestablishments categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 51 BC |
| Ab urbe condita | 703 |
| Armenian calendar | N/A |
| Bahá'í calendar | -1894 – -1893 |
| Bengali calendar | -643 |
| Berber calendar | 900 |
| Buddhist calendar | 494 |
| Burmese calendar | -688 |
| Byzantine calendar | 5458 – 5459 |
| Chinese calendar | 己巳年 (2586/2646) — to —
庚午年(2587/2647) |
| Coptic calendar | -334 – -333 |
| Ethiopian calendar | -58 – -57 |
| Hebrew calendar | 3710 – 3711 |
| Hindu calendars | |
| - Bikram Samwat | 6 – 7 |
| - Shaka Samvat | N/A |
| - Kali Yuga | 3051 – 3052 |
| Holocene calendar | 9950 |
| Iranian calendar | 672 BP – 671 BP |
| Islamic calendar | 693 BH – 692 BH |
| Japanese calendar | |
| Korean calendar | 2283 |
| Thai solar calendar | 493 |
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.