In 45 BC, Roman "dictator perpetuus" Julius Caesar defeated and killed king Juba I, and annexed his kingdom of Numidia to the Roman province, calling it Africa Nova ("New Africa"). This, however, dispossessed the ancient pro-Roman dynasty of Numidian kings founded by Massinissa, whose decision during the Second Punic War to switch allegiance from Carthage had been critical to the decisive Roman victory at the Battle of Zama 158 years earlier. The Numidian king's young son, Juba II, was brought up and educated at Rome, where he became a close friend of Caesar's grand-nephew Octavian, who assumed the title of Augustus after he became sole ruler of the Roman empire in 30 BC.