|Millennium:||1st millennium BC|
|Centuries:||2nd century BC – 1st century BC – 1st century|
|Decades:||70s BC 60s BC 50s BC – 40s BC – 30s BC 20s BC 10s BC|
|Years:||51 BC 50 BC 49 BC – 48 BC – 47 BC 46 BC 45 BC|
|48 BC by topic|
|Gregorian calendar||48 BC
|Ab urbe condita||706|
|Ancient Egypt era||XXXIII dynasty, 276|
|- Pharaoh||Cleopatra VII, 4|
|Ancient Greek era||183rd Olympiad (victor)¹|
|Chinese calendar||壬申年 (Water Monkey)
2649 or 2589
— to —
癸酉年 (Water Rooster)
2650 or 2590
|Coptic calendar||−331 – −330|
|Ethiopian calendar||−55 – −54|
|- Vikram Samvat||9–10|
|- Shaka Samvat||N/A|
|- Kali Yuga||3054–3055|
|Iranian calendar||669 BP – 668 BP|
|Islamic calendar||690 BH – 689 BH|
|Minguo calendar||1959 before ROC
|Seleucid era||264/265 AG|
|Thai solar calendar||495–496|
|Wikimedia Commons has media related to 48 BC.|
Year 48 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Caesar and Vatia (or, less frequently, year 706 Ab urbe condita). The denomination 48 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: Gaius Julius Caesar, Publius Servilius Vatia Isauricus.
- Civil War:
- January 4 – Caesar lands at Dyrrhachium (Durazzo).
- March – Mark Antony joins Caesar.
- April – Siege of Dyrrhachium, Caesar builds a fortified line of entrenchments and besiege Pompey.
- May – Publius Servilius Vatia Isauricus, co-consul with Julius Caesar, destroys Caelius's magistrate's chair on his tribunal.
- July 10 – Battle of Dyrrhachium, Julius Caesar barely avoids a catastrophic defeat to Pompey in Macedonia; he retreats to Thessaly.
- August 9 – Battle of Pharsalus: Caesar decisively defeats Pompey at Pharsalus and Pompey flees to Egypt. Pompey's army by and large pardoned.
- September 28 – Pompey the Great is assassinated on orders of King Ptolemy of Egypt after landing in Egypt (may have occurred September 29, records unclear).
- October – Julius Caesar reached Alexandria, city founded by Alexander the Great. He is met by an Egyptian delegation from Ptolemy XIII. The Egyptians offered him gifts: the ring of Pompey and his head.
- Caesar is named consul for a period of five years.
- Roman temple to Bellona on the Capitolinus outside Rome is burnt to the ground.
- Siege of Alexandria: Queen Cleopatra VII returns to the palace rolled into a Persian carpet and has it presented to Caesar by her servant. The Egyptian princess, only twenty-one years old, becomes his mistress.
- Pharnaces, King of Bosporus defeats Gnaeus Domitius Calvinus, a loyal partisan of Caesar, in the Battle of Nicopolis (or Nikopol).
- December – Battle in Alexandria, Egypt between the forces of Caesar and his ally Cleopatra VII and those of rival King Ptolemy XIII of Egypt and Queen Arsinoe IV. The latter two are defeated and flee the city, but during the battle part of the Library of Alexandria catches fire.
- Lucius Calpurnius Piso, consul under Caesar Augustus (d. AD 32)
- Consort Ban, Chinese concubine of Emperor Cheng of Han, also a female poet and scholar (d. 6 BC)
- September 29 – Pompey, Roman politician (assassinated) (b. 106 BC)
- Marcus Calpurnius Bibulus, Roman politician (b. c. 102 BC)
- Titus Annius Milo, Roman politician (died in exile)