Pinpointing the long-term causes of historical events is always a hazardous enterprise, and it might even be argued, at a rarefied and abstract level, that the conditions that prepared the ground for the accession of Caligula in AD 37 had been in continuous evolution since the earliest days of Rome’s founding, or even earlier. But few would dispute that a key event in that process, one signalling a more immediate prelude to his reign, was the Battle of Actium, in 31 BC. The victory of Caligula’s great-grandfather Octavian over the combined forces of Mark Antony, also his great-grandfather, and the Egyptian queen Cleopatra, left Octavian in effective control of the Roman world. Granted the title of Augustus in 27 BC, he proceeded to reshape the way that Rome and her territorial possessions were governed. It is common to refer to him as ‘emperor’ from that point on, but he aimed to project an image of a princeps, a first citizen in a reinvigorated republic, even though his initial bid for power was based on that most monarchical of claims, heredity. He was the designated heir and (posthumously) adopted son of Julius Caesar, who, in his lifetime, had been appointed perpetual dictator and had topped even that after death, by becoming a perpetual god. The system instituted by Augustus, briefly described earlier, in the Introduction, allowed him to remain the dominant force in Roman life until his death almost half a century later and offered, as compensation for the loss of political independence, an extended period of peace and stability. That system was still in force under Caligula, born two years before Augustus died, and, despite his appalling record, it survived him.