Year 55 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Crassus and Pompey (or, less frequently, year 699 Ab urbe condita). The denomination 55 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.
|Millennium:||1st millennium BC|
|Gregorian calendar||55 BC|
|Ab urbe condita||699|
|Ancient Egypt era||XXXIII dynasty, 269|
|- Pharaoh||Ptolemy XII Auletes, 26|
|Ancient Greek era||181st Olympiad, year 2|
|Balinese saka calendar||N/A|
|Chinese calendar||乙丑年 (Wood Ox)|
2642 or 2582
— to —
丙寅年 (Fire Tiger)
2643 or 2583
|Coptic calendar||−338 – −337|
|Ethiopian calendar||−62 – −61|
|- Vikram Samvat||2–3|
|- Shaka Samvat||N/A|
|- Kali Yuga||3046–3047|
|Iranian calendar||676 BP – 675 BP|
|Islamic calendar||697 BH – 696 BH|
|Minguo calendar||1966 before ROC|
|Seleucid era||257/258 AG|
|Thai solar calendar||488–489|
72 or −309 or −1081
— to —
73 or −308 or −1080
- Consuls: Marcus Licinius Crassus and Gnaeus Pompeius Magnus.
- Consuls Marcus Licinius Crassus and Gnaeus Pompeius Magnus pass the Lex Trebonia.
- Pompey's Theater, the first permanent (non-wooden) theatre in Rome is built. Built of stone on the Field of Mars, it included a temple to Venus Victorious, a public courtyard, and a meeting hall or curia in the far end near the "Sacred Area".
- Fourth year of Julius Caesar's Gallic Wars:
- Spring – Julius Caesar starts the season campaigning in Illyricum (in the Balkan region) against the Pirustae, who have been raiding Roman territory.
- Summer – Julius Caesar defeats the Usipetes and the Tencteri, two Germanic tribes who have been driven across the Rhine River by the Suebi. He spreads Roman law and order, and makes the whole country as far as the Channel accessible to trade.
- May – Julius Caesar defeats a Germanic army then massacres the women and children, totalling 430,000 people, near the Meuse and Rhine Rivers (now known as the city of Kessel in the Netherlands).
- June – Julius Caesar crosses the Rhine River near modern-day Koblenz. He constructs a wooden bridge between Andernach and Neuwied (Germany).
- August 22 or August 26 – Julius Caesar commands his first invasions of Britain, likely a reconnaissance-in-force expedition, in response to the Britons giving military aid to his Gallic enemies. Caesar retreats back to Gaul when the majority of his force is prevented from landing by storms.