The reign of Augustus as Rome's first emperor began in 27 BC with his first settlement with the Roman Senate, which granted him extraordinary proconsular powers, control over half of Rome's provinces and most of its armies, and the title of augustus ('the revered'). Prior to this event he is labeled by historians as Octavian (), having been born Gaius Octavius, before adopting the name of his great-uncle Gaius Julius Caesar, who named him as his primary heir in his will. In 30 BC Octavian defeated fellow Roman triumvir Mark Antony and his wife Cleopatra, Queen of the Ptolemaic Kingdom, conquering Egypt and bringing it under his personal possession. Styling himself as ('leading citizen', or 'first citizen'), Augustus sought to uphold the facade that he was a restorer of the Roman Republic, though his reign is viewed as the beginning of the Principate phase of the Roman Empire, which was ruled subsequently by members of his imperial family. After his death in AD 14, Augustus was deified and succeeded by his stepson and adopted son Tiberius.
During his second settlement with the Roman Senate in 23 BC, Augustus resigned from the consulship.Augustus was also known from the consulship and was not elected to this position again until 5 and 2 BC, so that he could help foster the political careers of his grandsons Gaius and Lucius Caesar. However, Augustus was granted the additional powers of the tribunate and censorship, holding these privileges for life and without formal election to either of these offices. He was granted authority to dictate affairs within the pomerium of Rome. Through his legates, he exercised direct control over provinces allotted to him by the Senate, but also interfered in the governance of provinces nominally controlled by the Senate through its proconsul governors. With the death of former triumvir Lepidus in 12 BC, Augustus assumed the title of ('supreme pontiff'), head of Rome's College of Pontiffs. In 2 BC, the Senate also conferred on Augustus the title of ('father of the country').
Augustus also conducted Rome's diplomacy. The Senate deferred to his decisions in the realm of foreign relations as he established peace treaties with the Parthian Empire in West Asia (to the east of Roman Syria) and the Kingdom of Kush in Northeast Africa (to the south of Roman Egypt). Augustus oversaw military campaigns in various regions. He completed the Roman conquest of Hispania with the Cantabrian Wars in the northern Iberian peninsula. In Southeastern and Central Europe, Augustus also ensured the Roman conquest and annexation of Dalmatia, Pannonia, Noricum, and Raetia. In Germania, Roman armies conquered as far as the Elbe River. However, with the defeat of Publius Quinctilius Varus by the forces of the Cherusci chief Arminius at the Battle of the Teutoburg Forest in AD 9, Augustus settled on defending the Rhineland as Rome's northern frontier.
Control of Egypt
In 31 BC Octavian's general Marcus Vipsanius Agrippa defeated the naval forces of Roman triumvir Mark Antony and his wife Cleopatra, Queen of Ptolemaic Egypt, at the Battle of Actium off the northwestern coast of Roman Greece. By August 30 BC the forces of Octavian defeated the forces of Antony and Cleopatra in Alexandria, after which Antony and then Cleopatra took their own lives. The conquest of Ptolemaic Egypt relieved the financial debts incurred by Octavian during the civil wars. He controlled Roman Egypt directly, forbade Roman Senators to travel there, and appointed equestrian governor Cornelius Gallus to supervise its administration and enormously lucrative taxation. While in Alexandria in 30 BC, Octavian visited the tomb of Alexander the Great, the conqueror king he emulated and associated himself with through similar artistic portraits. It is alleged in one ancient source that Octavian accidentally snapped off the nose of the body of Alexander in his tomb. Octavian's conquest of Ptolemaic Egypt brought an end to the Hellenistic period initiated by Alexander. It also cemented the cultural formation of a Greek East and Latin West in the Mediterranean and the type of cosmopolitan universal monarchy espoused by Alexander, albeit one now centered on Rome.
Octavian would become the first Roman emperor as Augustus and also the first Roman pharaoh of Egypt, though he did not partake in Egyptian coronation rites or worship of the Apis bull, and he never traveled to Egypt again after 30 BC. As historian Duane W. Roller explains, Augustus banned Egyptian religious rites within the city limits of Rome, but Egyptian style art and architecture spread in various forms to Rome itself under Augustus, seen in edifices such as the 15 BC pyramid tomb of Gaius Cestius. Historian Adrian Goldsworthy summarizes a xenophobic passage found in Virgil's epic poem the Aeneid about Octavian's conquest of Egypt, with the view that Actium was a "victory for the virtues and traditions of a united Italy supported by wholesome deities". He continues by writing that the enemy "were the chaotic forces of the east with their weird gods – the jackal-headed Anubis, god of the underworld, is singled out," even though Cleopatra and her Ptolemaic ancestors were Greek. Virgil also stressed how this victory brought about much needed peace and stability.
Before returning to Rome, Octavian spent the winter of 30 BC on the Greek island of Samos. In August 29 BC Octavian was awarded with three triumphs in Rome for his victories in Illyria, Greece, and Egypt. Octavian and Agrippa were elected as the consuls for 28 BC, and granted certain powers of the censor—but not with the office itself—for the duty of conducting Rome's census.
Principate
After Actium and the defeat of Antony and Cleopatra, Octavian was in a position to rule the entire Republic under an unofficial principate—with himself as ('leading citizen' or 'first citizen')—which he achieved through incremental power gains. He did so by courting the Senate and the people while upholding the republican traditions of Rome, maintaining the carefully curated appearance that he was not aspiring to dictatorship or monarchy. The term was previously applied to members of the Roman nobility who distinguished themselves in service to the Republic, and Octavian would embrace this title as part of his cultivated image as a restorer of the Republic.
Years of civil war had left Rome in a state of near lawlessness, but the Roman people were not prepared to accept the control of Octavian as a despot. At the same time, Octavian could not give up his authority without risking further civil wars. The Senate and people of Rome desired a return to stability, traditional legality, civility, and the assurance of free elections—which would be conducted in name at least under Octavian. Goldsworthy highlights this with the example of the Senate under consul Octavian decreeing that the doors to the Temple of Janus should be shut on 11 January 29 BC, a ritual that declared Rome was no longer at war, despite ongoing campaigns in Gaul and Hispania.
Goldsworthy stresses that Augustus did not have a carefully planned design in fashioning this principate regime, which was far from inevitable, and relied much on chance, experimentation, improvisation, and trial-by-error. Historian T. P. Wiseman argues that, given the overwhelmingly positive reception of Augustus in contemporary Roman sources, Augustus should not be viewed as an unlawful usurper masking his monarchical intentions or autocratic wishes. Patricia Southern surmises that Octavian needed to at least keep up the appearance of being bound by term limits for the consulship and other offices: "Octavian probably remembered very starkly that Caesar did not survive for more than a few weeks after accepting the appointment as ". With the exception of Sulla, Gaius Julius Caesar had been elected as dictator for unprecedented lengths of time, with a one year term in 48 BC, a ten-year term in 46 BC, and finally as ('dictator in perpetuity') in 44 BC, a month before his assassination on the Ides of March.
First settlement
Patronage
On 13 January 27 BC, Octavian made a show of returning full power to the Senate and relinquishing his control of the Roman provinces and their armies. Octavian was no longer in direct control of the provinces and their armies, but he retained the loyalty of soldiers and veterans alike. The careers of many clients and adherents depended on his patronage, as his financial power was unrivaled in the Roman Republic. On this, the historians Werner Eck and Sarolta Takács state that:
To a large extent, the public was aware of the vast financial resources that Octavian commanded. He failed to encourage enough senators to finance the building and maintenance of networks of roads in Italy in 20 BC, but he undertook direct responsibility for them. This was publicized on the Roman currency issued in 16 BC, after he donated vast amounts of money to the , the public treasury.
Control of provinces Octavian's power was ultimately rooted in his control over Rome's military and ability to eliminate the opposition by force if necessary. The Senate proposed to Octavian, the victor of Rome's civil wars, that he once again assume command of the provinces. The Senate's proposal was a ratification of Octavian's extra-constitutional power. Through the Senate, Octavian was able to continue the appearance of a still-functional constitution. Feigning reluctance, on 16 January 27 BC he accepted a ten-year responsibility of overseeing provinces that were considered chaotic. The provinces ceded to Augustus for that ten-year period constituted much of the Roman world, including all of Hispania and Gaul, Syria, Cilicia, Cyprus, and Egypt. Moreover, command of these provinces provided Augustus with control over the majority of Rome's legions. This agreement with the Senate is known as the first settlement, in which Octavian—now Augustus—was granted imperial powers and had his autocratic authority officially recognized, while maintaining the appearance that he had restored the Republic and gave power back to the Senate.
Octavian-Augustus became the most powerful political figure in the city of Rome and its provinces, but he did not have a monopoly on political and martial power. The Senate still controlled North Africa, an important regional producer of grain, as well as Illyria and Macedonia, two strategic regions with several legions. However, the Senate had control of only five or six legions distributed among three senatorial proconsuls, compared to the twenty legions under the control of Augustus, and their control of these regions did not amount to any political or military challenge to Augustus. Nevertheless, the Senate sharing control over the provinces with Augustus was not without precedent during the Republic, and Augustus operated within republican legal frameworks to amass his power. Augustus's control of entire provinces even followed Republican-era precedents for the limited objective of securing peace and creating stability. For instance, Pompey had been given a similar level of command across the Roman world, including control over military operations across all Mediterranean shorelines extending 50 miles inland, and possibly greater authority than provincial governors in these areas. Pompey was given term limits for extraordinary proconsular authority that included legates who answered to him, not the Senate, during his campaign against Mediterranean pirates in 67 BC and the subsequent Third Mithridatic War against Mithridates VI of Pontus.