Mark Antony was military commander for Julius Caesar during his conquest of Gaul and administrator of Italy while Caesar eliminated his opponents in Greece, Africa, and Spain. After Caesar's assassination in 44 B.C., Antony joined Lepidus and Caesar's adoptive son Octavian in a three-man dictatorship known as the Second Triumvirate. They defeated Caesar's murderers, the Liberatores, at the Battle of Philippi in 42 B.C. and divided the Republic among themselves. Antony took the east, including Egypt, ruled by Queen Cleopatra, and command of Rome's war against Parthia. Relations within the Triumvirate were strained but civil war was averted when Antony married Octavian's sister Octavia. Despite the marriage, Antony continued his affair with Cleopatra and even married her. The Triumvirate broke up in 33 B.C. and erupted into civil war in 31 B.C. At Octavian's direction, the Roman Senate declared war on Cleopatra and proclaimed Antony a traitor. Octavian defeated Antony at the Battle of Actium the same year. Defeated, Antony and Cleopatra fled back to Egypt where they committed suicide. With Antony dead, Octavian was the undisputed master of the Roman world and would reign as the first Roman emperor with the title Augustus.