Year 43 BC was either a common year starting on Sunday, Monday or Tuesday or a leap year starting on Sunday or Monday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a common year starting on Monday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Pansa and Hirtius (or, less frequently, year 711 Ab urbe condita). The denomination 43 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 Vibius Pansa Caetronianus and Aulus Hirtius. The Roman Senate confirms Octavian as propraetor with joint responsibility for the campaign against Antony. Hirtius and Octavian mobilize troops for the march to Mutina, while Pansa continues the levy. Embassy dispatched to treat with Antony.
- Gaius Antonius is defeated by Marcus Junius Brutus at Dyrrachium. Brutus proceeds to secure his position in Thrace and Macedonia. Gaius Cassius Longinus campaigns in Syria and defeats the army of Publius Cornelius Dolabella at Laodicea.
- March – Vibius Pansa set out to link up with Hirtius and Octavian, bringing four legions of recruits, having left one, the legio urbana, to defend Rome.
- April 14 – Battle of Forum Gallorum: Mark Antony, besieging Caesar's assassin Decimus Brutus in Mutina, defeats the forces of the consul Pansa, but is then immediately defeated by the army of the other consul, Hirtius. Both consuls are killed (Hirtius does not die until after the Battle of Mutina).
- April 21
- Antony marches to Parma (which is sacked) and Placentia. He then crosses the Ligurian Alps to Vada Sabatia, 50 km (31 mi) south-west of Genoa, and joins with Aemilius Lepidus, soon after Decimus Brutus is killed by brigands. The Senate declares Antony a hostis, an enemy of the state. Sextus Pompey becomes supreme commander of the Roman navy and Gaius Cassius proconsul of Syria.
- Summer – Gaius Cassius captures Rhodes after refusing paying tribute. Their fleet is defeated by Roman galleys in the Aegean Sea. He lands a military force on the island and plunders the city. Cassius puts to death 50 of the leading citizens and seizes all the gold he could lay hands on.
- July–August – Antony is again at the head of a large army; Octavian enters Rome in force without opposition. It is clear that Cicero's plan to divide them against each other has failed.
- August 19th – Gaius Octavian taking office as consul, the day before his 20th birthday, is prevailed to pass the lex Pedia, a law establishing the murder of Caesar as a capital crime.
- November 26 – Octavian meets Antony and Lepidus in Bononia and the three enter into an official five-year autocratic pact, the Second Triumvirate (see lex Titia). To cement their reconciliation Octavian agrees to marry Clodia, a daughter of Antony's wife Fulvia by her former husband Publius Clodius Pulcher.
- November – The triumvirs introduce proscriptions in which allegedly 130 senators and 2,000 equites are branded as outlaws and deprived of their property.
- December 7 – Marcus Tullius Cicero is killed in Formiae in a litter going to the seaside, by a party led by Herennius (a centurion) and Popilius (a military tribune). His head and hands are displayed on the Rostra in the Forum Romanum.
- April 22 – Gaius Vibius Pansa, Roman consul and general (killed in battle)
- December 7 – Cicero, Roman statesman and orator (murdered) (b. 106 BC)
- Antipater the Idumaean, Jewish founder of the Herodian Dynasty (murdered)
- Atia Balba Caesonia, niece of Julius Caesar and mother of Augustus (b. 85 BC)
- Aulus Hirtius, Roman consul and historian (killed in battle)
- Decimus Brutus, Roman statesman (murdered) (b. c. 85 BC)
- Decimus Laberius, Roman nobleman and Latin writer (b. c. 105 BC)
- Gaius Trebonius, Roman politician (assassin of Julius Caesar)
- Gaius Verres, Roman politician and governor (b. c. 120 BC)
- Lucius Calpurnius Piso, Roman consul and governor (b. c. 100 BC)
- Lucius Minucius Basilus, Roman politician (assassin of Julius Caesar)
- Lucius Roscius Fabatus, Roman politician (killed in battle)
- Pontius Aquila, Roman politician (assassin of Julius Caesar)
- Publius Cornelius Dolabella, suffect consul after the assassination of Julius Caesar (b. 70 BC)
- Publilius Syrus, Syrian comic dramatist and Latin writer
- Quintus Pedius, suffect consul after the assassination of Julius Caesar
- Quintus Tullius Cicero, Roman statesman and general (b. 102 BC)
- Servius Sulpicius Rufus, Roman politician and jurist (b. c. 106 BC)
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- ^ Warfare in the Classical World, John Warry (1980), p. 177. ISBN 0-8061-2794-5
- ^ Haskell, H. J.: This was Cicero (1964), p. 293