The Battle of Actium was the decisive confrontation of the Final War of the Roman Republic. It was a naval engagement fought between the forces of Octavian and the combined forces of Mark Antony and Cleopatra VII. The battle took place on 2 September 31 BC, on the Ionian Sea near the city of Actium, at the Roman province of Epirus vetus in Greece. Octavian's fleet was commanded by Marcus Vipsanius Agrippa, while Antony's fleet was supported by the ships of Queen Cleopatra of Ptolemaic Egypt.

Octavian's victory enabled him to consolidate his power over Rome and its dominions. To that end, he adopted the title of Princeps ("first citizen") and some years after the victory was awarded the title of Augustus ("revered") by the Roman Senate. This became the name by which he was known in later times. As Augustus, he would retain the trappings of a restored Republican leader; however, historians generally view this consolidation of power and the adoption of these honorifics as the end of the Roman Republic and the beginning of the Roman Empire.