The Second Triumvirate of Marc Antony, Octavian and Marcus Lepidus emerged out of the civil war that had erupted following the assassination of Julius Caesar in 44 BC.
However, the power-sharing agreement broke down as Antony grew closer to Queen Cleopatra VII Egypt. He eventually separated from his wife Octavia - Octavian’s sister - in favour of the Egyptian queen and together they along with Caesarion, Cleopatra’s son by Julius Caesar, were soon portrayed as a threat to the stability of the Roman Republic.
Swayed by the publication of Antony’s will, which had come into Octavian’s hands after the defection of Plancus, the Senate declared war against Cleopatra in 31 BCE. It was clear that Antony too would be drawn into battle and, on 2 September the opposing forces met for the decisive naval battle outside the Gulf of Actium in Greece.
Antony’s fleet of larger ships was undermanned due to a malaria outbreak, which meant that they were easily out-manoeuvred by Octavian’s smaller “Liburnian” vessels. Octavian further benefited from the defection of Antony’s General, Quintus Dellius, who brought with him Antony’s plans.
Both sides attempted to outflank the other for much of the afternoon without any decisive breakthrough. Eventually Cleopatra’s Egyptian galleys, which had stayed behind Antony’s fleet, fled the battle. Antony followed soon afterwards, and the remainder of his fleet were forced to surrender.
Antony’s land forces deserted him as Octavian advanced on Egypt. Both Antony and Cleopatra subsequently committed suicide, leaving Octavian to consolidate his control over Rome.