The transition of Rome from a Republic to an Empire was a gradual one. The transfer of political power from the Roman senate into the hands of the Emperor and the army began during the career of Julius Caesar and was complete during the life of Augustus Caesar, his heir. The period surrounding the career of the first two caesars is exceptionally dramatic and features several of the most famous characters and most consequential battles, in Roman history.
In the years following the Civil War of Marius and Sulla, several important political leaders arose. Julius Caesar, who as a young man had fled from Sulla's proscriptions, returned to Roman and gradually began to gain great influence with the populares party. On the side of the aristocrats, Cicero and Cato (the younger) arose. Cicero was an influential senator, known for putting down the Catiline conspiracy, an attempt by the populares to overthrow the republican government. Cicero was a prolific writer, and one of the best primary sources of this period of Roman history. Both Cicero and Cato were sincere republicans and well-versed spokesmen for the best ideals of republican government, but in spite of their sincere convictions and personal rectitude, they were unable to maintain power in an age of dictators and demagogues.
In 60 B.C. Crassus, Pompey , and Caesar put aside their political differences and formed the First Triumvirate, in which they divided the empire into three regions: Crassus help power in the east, Caesar in Hispania, and Pompey in Rome. Crassus soon perished on an ill-fated campaign in Parthia, leaving Pompey and Caesar in power. Caesar's enemies sought to send him far off to the western frontier to get him out of the way, but this proved a tremendous miscalculation. Caesar, who up to this time had no particular military experience, took this charge seriously and in the six years from 58 to 52 B.C., he led the Roman Conquest of Gaul, which brought the entire region of Gaul (modern France), under his sway. This was the greatest addition of Roman territory in over a century, and it brought him unbounded prestige and popularity within Rome and the army.
Caesar's enemies in Rome tried to deprive him of his legions and bring him back under control, but it was too late. In 49 B.C. Caesar crossed the Rubicon with his army and marched on Rome, thereby provoking the Caesarean Civil War. Yet so great was his popularity that no army rose against him, and his enemies, including Pompey, fled to the east. Unlike his predecessors, Caesar ordered no purge of his political enemies, and in many ways tried hard to win over and reconcile them. He had an all-encompassing vision for the administration of an empire that had animated his actions for many years, and as soon as he came to power, he started implementing many of his reforms.
Although Caesar controlled the west with very little opposition, Pompey and his legions still held sway in the east. Caesar eventually raised an army to meet Pompey and beat him decisively at the Battle of Pharsalia. He did not seek to kill Pompey but desired to reconcile with him. Caesar pursued Pompey to Egypt, where Pompey was murdered by traitors. While in Egypt, Caesar became involved with Cleopatra and fought the Battle of Alexandria in order to secure her place on the Egyptian throne. He eventually returned to Rome, and began implementing his reforms in earnest, but in spite of all the effort he had put into reconciling with his enemies, a conspiracy formed against him. He was assassinated in the senate only five years after crossing the Rubicon, but his vision for a military based, centrally-administered empire survived him.
Augustus Caesar is usually considered the first Roman emperor because under his long reign Rome became reconciled to its new form of government. Rome had seen several dictators in the previous years, and the ideals of republican government had already given way, but it was not until the reign of Augustus that stability, peace, and prosperity returned to the government, and active opposition to the new regime ceased. Augustus, then known as Octavius, came to power in 43 B.C., shortly after the death of his uncle Julius Caesar. Although a young man, he was Caesar's heir, and by patience and persistence he was able to wrest enough power from Antony to establish himself as a joint ruler of Rome, part of the Second Triumvirate.
Octavius spent the early years of his reign consolidating power. This involved using force when necessary, as when he and Antony crushed the Republican opposition lead by Marcus Brutus and Cassius at the Battle of Philippi. But most of the time he followed the example of his uncle Julius Caesar, trying to reconcile his enemies. After Philippi, Octavius ruled jointly with Antony, but their relationship soured as a result of Antony's long and irresponsible dalliance with Cleopatra. Finally the two rulers, now bitter enemies, met at the Battle of Actium in 31 B.C. From this point until his death in 14 A.D., Octavius was sole ruler of the Roman Empire, although he was not declared Augustus for several more years.
Once Octavius' power was established, he followed through on many of Caesar's plans for the empire, including transferring administrative responsibility for most provinces to the army, tax reform, encouraging immigration, and investing in infrastructure and public works. Augustus and his advisor, Maecenas, were patrons of the arts, and under his reign literature flourished. The Latin poets Horace and Virgil, the historian Livy, and many other artists ushered in a great era of Latin literature and scholarship.