On September 2, 31 BC, at the Battle of Actium, the decisive naval battle that ended the Roman Republic took place. Octavian's forces defeated those under Mark Antony and Cleopatra off the western coast of Greece. From the article:
"The Battle of Actium
At the Battle of Actium, off the western coast of Greece, Roman leader Octavian wins a decisive victory against the forces of Roman Mark Antony and Cleopatra, queen of Egypt. Before their forces suffered final defeat, Antony and Cleopatra broke though the enemy lines and fled to Egypt, where they would commit suicide the following year.
With the assassination of Roman dictator Julius Caesar in 44 B.C., Rome fell into civil war. To end the fighting, a coalition–the Second Triumvirate–was formed by three of the strongest belligerents. The triumvirate was made up of Octavian, Caesar’s great-nephew and chosen heir; Mark Antony, a powerful general; and Lepidus, a Roman statesman. The empire was divided among the three, and Antony took up the administration of the eastern provinces. Upon arriving in Asia Minor, he summoned Queen Cleopatra to answer charges that she had aided his enemies. Cleopatra, ruler of Egypt since 51 B.C., had once been Julius Caesar’s lover and had borne him a child, who she named Caesarion, meaning “little Caesar.”
Cleopatra sought to seduce Antony as she had Caesar before him, and in 41 B.C. arrived at Tarsus on a magnificent river barge, dressed as Venus, the Roman goddess of love. Successful in her efforts, Antony returned with her to Alexandria, where they spent the winter in debauchery. In 40 B.C., Antony returned to Rome and married Octavian’s sister Octavia in an effort to mend his increasingly strained relationship with Octavian. The triumvirate, however, continued to deteriorate. In 37 B.C. Antony separated from Octavia and traveled to the East, arranging for Cleopatra to join him in Syria. In their time apart, Cleopatra had borne him twins, a son and a daughter. According to Octavian’s propagandists, the lovers were then married, which violated the Roman law restricting Romans from marrying foreigners.
Antony’s disastrous military campaign against Parthia in 36 B.C. further reduced his prestige, but in 34 B.C. he was more successful against Armenia. To celebrate the victory, he staged a triumphal procession through the streets of Alexandria, in which Antony and Cleopatra sat on golden thrones, and their children were given imposing royal titles. Many in Rome, spurred on by Octavian, interpreted the spectacle as a sign that Antony intended to deliver the Roman Empire into alien hands.
After several more years of tension and propaganda attacks, Octavian declared war against Cleopatra, and therefore Antony, in 31 B.C. Enemies of Octavian rallied to Antony’s side, but Octavian’s brilliant military commanders gained early successes against his forces. On September 2, 31 B.C., their fleets clashed at Actium in Greece. After heavy fighting, Cleopatra broke from the engagement and set course for Egypt with 60 of her ships. Antony then broke through the enemy line and followed her. The disheartened fleet that remained surrendered to Octavian. One week later, Antony’s land forces surrendered.
Although they had suffered a decisive defeat, it was nearly a year before Octavian reached Alexandria and again defeated Antony. In the aftermath of the battle, Cleopatra took refuge in the mausoleum she had had built for herself. Antony, informed that Cleopatra was dead, stabbed himself with his sword. Before he died, another messenger arrived, saying Cleopatra still lived. Antony was carried to Cleopatra’s retreat, where he died after bidding her to make her peace with Octavian. When the triumphant Roman arrived, she attempted to seduce him, but he resisted her charms. Rather than fall under Octavian’s domination, Cleopatra committed suicide, possibly by means of an asp, a poisonous Egyptian serpent and symbol of divine royalty.
Octavian then executed Cleopatra’s son, Caesarion, annexed Egypt into the Roman Empire, and used Cleopatra’s treasure to pay off his veterans. In 27 B.C., Octavian became Augustus, the first and arguably most successful of all Roman emperors. He ruled a peaceful, prosperous, and expanding Roman Empire until his death in 14 A.D. at the age of 75."