This article concerns the period 39 BC – 30 BC.
- Marcus Antonius dispatched Publius Ventidius Bassus with 11 legions to the East and drives Quintus Labienus out of Asia Minor, he retreats into Syria, where he received Parthian reinforcements. Ventidius finally defeats him in the battle at the Taurus Mountains.
- Publius Ventidius defeats Pharnastanes with his cataphracts at the Amanus Gates, and goes on to reclaim Syria, Phoenicia and Judea. Labienus flees to Cilicia, where he is captured and executed.
- Sextus Pompey, styled himself "son of Neptune", controlled Sicily, Sardinia, Corsica and the Peloponnesus is recognized by the Triumvirate in the Pact of Misenum. The pact helped to assure Rome's grain supply, the blockade on Italy is lifted.
- January 1 – Beginning of the Hispanic era, by orders of Octavian Caesar.
- January 17 – Octavian marries Livia while she is still pregnant from a recently broken marriage. Octavian gained permission from the College of Pontiffs to wed her while she was still pregnant from another husband. Three months after the wedding she gave birth to a second son, Nero Claudius Drusus, while he and his elder brother, the four-year-old Tiberius, lived in Octavian's household.
- Octavian appointed Marcus Vipsanius Agrippa governor of Transalpine Gaul, where he put down an uprising of the Aquitanians. He also fought successfully against the Germanic tribes, and becoming the next Roman general to cross the Rhine after Julius Caesar.
- Mark Antony, Gaius Julius Caesar Octavianus and Marcus Lepidus sign the Treaty of Tarentum (or 37 BC), extending the Second Triumvirate until 33 BC.
- Parthian invasion into Roman Syria; Publius Ventidius Bassus defeats Pacorus, at the crossing of the Euphrates in the Battle of Cyrrhestica. Ventidius lays siege to Antiochus I Theos of Commagene in Samosata until relieved by Antony.
- Consuls: Marcus Vipsanius Agrippa and Titus Statilius Taurus.
- Agrippa created the harbour "Portus Julius" in the today submersed town of Puteoli (the modern Pozzuoli, close to Naples). The port is used to train the warships for naval battles, a new fleet is built, with 20,000 oarsmen gathered by freeing slaves. He also incorporated on quinqueremes a technical innovation the harpax ("snatcher"); a combination ballista and grappling hook, based on the corvus.
- Gaius Julius Caesar Octavian engineered the "Second Pact of Tarentum" which renewed the Triumvirate for an additional five years. Mark Antony exchanged 120 ships, for service against Sextus Pompeius. Octavian Caesar gives 1,000 troops from the Praetorian Guard and 20,000 legionaries for the Parthian campaign in Syria.
- Antony reorganized Asia Minor under strongmen loyal to him. He raised troops from his allies Amyntas and Archelaus, kings of Galatia and Cappadocia. The old kingdom of Pontus is restored, from Armenia to the River Halys under Polemon I.
- Romans conquer Jerusalem from the Parthians. Herod the Great becomes king of Judea and Ananelus is installed as High Priest, both positions seized from Antigonus II Mattathias after a five-month siege. Thousands of Jews slaughtered by Roman troops supporting Herod.
- Consuls: Lucius Gellius Publicola and Marcus Cocceius Nerva.
- Publius Canidius Crassus invaded Armenia and Iberia (Georgia); he forced Parnavaz II into an alliance against Zober, king of Albania.
- June – Mark Antony launches a major offensive against the Parthians, he marches with 10 legions and 10,000 cavalry to Carana in Anatolia.
- July – Octavian's fleet (102 warships) embarked from Puteoli and tried to invade Sicily, it is caught in a storm and forced to return at Vibo.
- August – Marcus Vipsanius Agrippa, an admiral of Octavian Caesar, secures the Lipari Islands and harasses the coast from Mylae to Tyndaris. Octavian transports his legions via Leucopetra to Tauromenium (modern Taormina).
- Antony crosses the frontier into Media Atropatene and commences the siege of Phraaspa. He established a line of circumvallation and built siege engines.
- September 3 – Battle of Naulochus: Agrippa defeats Sextus Pompeius, a son of Pompeius, in a naval engagement off Naulochus. Sextus escapes with 17 ships to Messana and then to Asia Minor.
- Marcus Lepidus lands 12 legions from Africa and lays siege to Lilybaeum. He loses his army to Octavian when his men mutiny. Lepidus is kept in luxurious captivity in Rome until his death.
- Agrippa receives the unprecedented honor of a Naval Crown (corona navalis), wrought of gold and decorated with the prows of ships.
- October – Antony abandons the siege of Phraaspa (near Maragheh, Iran). He retreats, loses many men to disease and starvation in the subsequent retreat to Egypt, marries Cleopatra VII while still married to Octavia.
- Judea: Aristobulus III, the last of the Hasmoneans, becomes High Priest in Jerusalem, replaces Ananelus, who only held the position for one year.
- Gnaeus Domitius Ahenobarbus and Gaius Sosius become Roman Consuls.
- Spring – Final War of the Roman Republic: Mark Antony transfers his headquarters from Samos to Athens; he assembles a fleet of 500 combat vessels and 300 transport ships, crewed by 150,000 men.
- Sparta under Caius Iulius Eurycles, whose father Antony had ordered to be executed for piracy, declares his support for Octavian. Lappa (modern Argyroupoli) in Attica and Kydonia in Crete revolt against Cleopatra.
- July – The Roman Senate declares war upon Mark Antony and Cleopatra VII. Octavian Caesar is proclaimed dux and the West: Gallic and Spanish provinces, Africa, Sicily and Sardinia swears an oath (sacramentum) of loyalty to him. In order to assure this oath, Octavian forces the high priest of the Vestal Virgins in Rome to hand over Antony's will, which give information over the Roman-conquered territories as kingdoms and plans to build a tomb in Alexandria for him and Cleopatra.
- Winter – Antony distributes garrisons along the west coast of Greece, stations the fleet at Actium and establishes his headquarters at Patrae.
- Zacynthus is held by Gaius Sosius, Methone (Messenia) by Bogud of the royal house of Mauretania, driven into exile by his brother Bocchus II.
- Gaius Julius Caesar Octavian becomes Roman Consul for the third time. His partner is Marcus Valerius Messalla Corvinus, replacing Mark Antony
- Octavian crosses the Strait of Otranto and lands with an army (15 legions) at Panormus in Dalmatia. He marches to Toryne in the south, and establishes a bridgehead at the Gulf of Ambracia.
- Marcus Vipsanius Agrippa sails with 300 war galleys to the western Peloponnese, and occupies strategic positions around the Gulf of Corinth to cut off Antony's line of communication.
- Antony, alerted by Octavian's presence, sets up camp on the southern shore, at the promontory of Actium. He dispatches a force to isolate the camp of Octavian in the valley of Louros.
- Agrippa storms Leucas, giving Octavian an anchorage and a second depot for his land supplies. He seizes the garrison at Patrae, and takes Antony's headquarters.
- Amyntas, king of Galatia, deserts with 2,000 cavalry to Octavian. One-third of Antony's oarsmen are lost to malnutrition, disease and desertion.
- September 2 – Roman Civil War: Battle of Actium: Off the western coast of Greece, Octavian Caesar defeats naval forces under Mark Antony and Cleopatra VII.
- The Egyptian fleet (60 warships), including Cleopatra's treasure ship retreats to Taenarus, Antony transfers his flag to a smaller vessel and breaks through Octavian's line.
- Winter – Octavian (32 years old) takes court at Samos. After his decisive victory at Actium he builds Nicopolis; the city is populated by Greeks from settlements further inland.
- Possible date of composition of the Tirukkuṛaḷ, attributed to Thiruvalluvar.
- First possible date for the invention of the wheelbarrow in history; as the 5th century Book of the Later Han states that the wife of the once poor and youthful imperial censor Bao Xuan of the Chinese Han dynasty helped him push a lu che back to his village during their feeble wedding ceremony, around this year.
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