The predecessor state of the Roman Empire, the Roman Republic (which had replaced Rome's monarchy in the 6th century BC) became severely destabilized in a series of civil wars and political conflicts. In the mid-1st century BC, Julius Caesar was appointed as perpetual dictator and then assassinated in 44 BC. Civil wars and proscriptions continued, eventually culminating in the victory of Octavian, Caesar's adopted son, over Mark Antony and Cleopatra at the Battle of Actium in 31 BC. The following year Octavian conquered Ptolemaic Egypt, ending the Hellenistic period that had begun with the conquests of Alexander the Great of Macedon in the 4th century BC. Octavian's power then became unassailable, and in 27 BC the Roman Senate formally granted him overarching power and the new title "Augustus", effectively making him the first Roman emperor.