The Battle of Actium was the decisive engagement in the Final War of the Roman Republic between the forces of Octavian and the combined forces of Mark Antony and Cleopatra. It was fought on September 2, 31 BC, on the Ionian Sea near the Roman colony of Actium in Greece. Octavian's fleet was commanded by Marcus Vipsanius Agrippa, while Antony's fleet was supported by the fleet of his lover, Cleopatra VII, queen of Ptolemaic Egypt.
The victory of Octavian's fleet enabled him to consolidate his power over Rome and its domains, leading to his adoption of the title of Princeps ("first citizen") and his accepting the title of Augustus from the Senate. As Caesar Augustus, he would preserve the trappings of a restored Republic, but many historians view his consolidation of power and the adoption of his honorifics flowing from his victory at Actium as the end of the Roman Republic and the beginning of the Roman Empire.
The two fleets met outside the Gulf of Actium, on the morning of September 2, 31 BC, with Mark Antony leading 230 warships through the straits toward the open sea. Waiting beyond the straits was the fleet of Octavian, led by the experienced admiral Agrippa, who commanded from his position on the left wing of the fleet. Lucius Arruntius commanded the centre of Octavian's fleet while Marcus Lurius commanded the right. Octavian's armies watching from shore to the north of the straits were under the command of Statilius Taurus.
Mark Antony and Gellius Publicola commanded the right wing of the Antonian fleet, while Marcus Octavius and Marcus Insteius commanded the centre, with Cleopatra's squadron positioned behind them. Gaius Sosius launched the initial attack of the battle from the left wing of the fleet, while Antony's chief lieutenant Publius Canidius was left in charge of the triumvir's land forces.
Octavian's fleet was comprised largely of smaller, fully-manned Liburnian vessels, armed with better-trained and fresher crews. His ships were also lighter and could protect themselves by out-manoeuvring the quinqueremes in Roman naval battle, where one objective was to ram the enemy ship and at the same time kill the above deck crew with a shower of arrows and catapult-launched stones large enough to decapitate a man. Prior to the battle, a general of Mark Antony known as Quintus Dellius had defected to Octavian and brought with him Mark Antony’s battle plans. Antony had hoped to use his biggest ships to drive back Agrippa's wing on the north end of his line, but Octavian's entire fleet stayed carefully out of range. Shortly after mid-day, Antony was forced to extend his line out from the protection of the shore, and then finally engage the enemy.
Seeing that the battle was going against Antony, Cleopatra's fleet retreated to open sea without participating. Mark Antony retreated to a smaller vessel with his flag and managed to escape the battle, taking a few ships with him as an escort to help break through Octavian's lines. Those that he left behind, however, were not so fortunate: Octavian's fleet captured or sank all of them.
Another theory about the battle suggests that Antony knew he was surrounded and had nowhere to run. Antony gathered his ships around him in a quasi-horseshoe formation, staying close to the shore for safety. If Octavian's ships tried to approach Antony's, the sea would push them into the shore. Antony may have known that he would not be able to defeat Octavian's forces, so he and Cleopatra stayed in the rear of the formation. Eventually, Antony sent the ships on the northern part of the formation to attack. He had them move out to the north, spreading out Octavian's ships which up until now were tightly arranged. He sent Gaius Sosius down to the south to spread the remaining ships out to the south. This left a hole in the middle of Octavian's formation. Antony seized the opportunity and with Cleopatra on her ship and him on a different ship, sped through the gap and escaped, abandoning his entire force.
The political consequences of this sea battle were far-reaching. As a result of the loss of his fleet, Mark Antony's army, which had begun as equal to that of Octavian, deserted in large numbers. Antony lost some 19 infantry legions and 12,000 cavalry under cover of darkness before he had any chance to engage Octavian on land. Despite a victory at Alexandria on July 31, 30 BC, more of Mark Antony's armies eventually deserted him, leaving him without a competent force to fight Octavian. Mark Antony then tried to flee from the battle. In a communication breakdown, Antony came to believe that Cleopatra had been captured, and so he committed suicide.
Cleopatra heard the news about Mark Antony and, rather than risk being captured by Octavian, committed suicide herself, on August 12, 30 BC. She allowed herself to be bitten by a poisonous asp that was reportedly hidden for her in a basket of figs. Octavian had Caesarion killed later that year, securing his legacy as Julius Caesar's only 'son'.
Thus, Octavian's victory at the Battle of Actium captured sole and uncontested control of the Roman domains of the Mediterranean; he became "first citizen" of Rome. This victory enabled his consolidation of power over every institution of Roman administration, as "Augustus Caesar", marking the transition of Rome from Republic to Empire. The final surrender of Egypt and the death of Cleopatra also marks, for many historians, the final demise of both the Hellenistic Age and the Ptolemaic Kingdom.
To commemorate his victory over Antony, Augustus established the Roman festival Actia. Augustus also erected a monument overlooking the site, which incorporated the bronze rams taken from the defeated ships. The surviving sockets in the stonework evidence the considerable size of these rams.