Caesar returned to Rome in 73 BC as a member of the college of Pontiffs and immediately began working on his political career. He lived well beyond his means, and started down a course of extravagance, both for political gain and personal pleasure. From expensive slaves to collectible arts, Caesar spared no expense in creating an image of an elite member of Roman society. Within a year he was elected as a military tribune. Though his service in the east likely already pre-empted the need to prove himself in a military capacity, it was nevertheless an important step in validating military capability. It's possible, though the history of Caesar's career at this point is limited, that he may have begun his acquaintance with Marcus Licinius Crassus as this point. There is a high probability that he served under Rome's richest man during his command against Spartacus and the slave rebellion.
Whether he served directly under Crassus, or developed a friendship though other associations, the friendship would be pivotal to Caesar's career. Because of Crassus' immense wealth, Caesar was able to finance the extravagant lifestyle and political necessities required to advance the cursus honorum. His next step was that of Quaestor which he was elected to in 69 BC. In this term he was assigned to the governor of Further Spain, Antistius Vetius but tragedy, or an opportunity struck before he could depart Rome. His aunt Julia, wife of Marius, died about this same time and Caesar took the opportunity to break Roman tradition.
Women generally were not granted large public funerals, but in the case of some influential individuals, tradition was broken. In the extravagant public funeral (laudation) that followed, Caesar pushed the extremes of the Optimate Senators limits. He not only praised his aunt in a stirring public speech, but for this first time since Sulla, he displayed the popular images of Gaius Marius. Praising the deeds of Marius, and publicly proclaiming his descent from the fourth King of Rome, Ancus Marcius, and the goddess Venus, he certainly developed considerable enmity among the conservative Senators. Still though, the crowd was clearly in Caesar's favor as they supported him enthusiastically, even drowning out attempts by the Senate to stop the young Quaestor. Caesar clearly defined himself as a populares, setting the stage for many political battles to come.
Shortly after the grand event of his aunt's funeral, more personal tragedy struck. This time his young wife Cornelia died, the mother of his single infant daughter, Julia. To give a laudation for such a young women was practically unspeakable, but once again Caesar rose to the challenge presented by conservative opposition. In another stirring public ceremony, Caesar honored Cornelia's father, Cinna, another hated enemy of the optimates. The young man was not only building a considerable reputation for anti-establishment government, but was winning the hearts of the people through his emotional and powerful public displays.
Soon after the funerals, Caesar finally left to join Vetius in Spain. As an administrative and financial officer, the trip was largely uneventful, but it was here that he had the famous encounter with a statue of Alexander the Great. Perhaps because of his weakened emotional state coupled with a growing and now obvious personal ambition, he had a definitive and prophetic reaction to the site of the statue. At the temple of Hercules in Gades, it was said that he either broke down and cried or at the very least was deeply saddened in reaction to it.. When asked why he would have such a reaction, his simple response was: "Do you think I have not just cause to weep, when I consider that Alexander at my age had conquered so many nations, and I have all this time done nothing that is memorable."
At any rate, Caesar was soon allowed to return to Rome, released early from his duties. While returning, he began to nurture his relationship with the common man even further. Identifying with the people of Cisalpine Gaul, who had felt oppressed since the time of Sulla, Caesar may have encouraged a revolt. It's difficult to determine what, if any role Caesar may have actually played, but it's sufficient to note that while he was accused of treason, he was not convicted. Other than building more enmity between himself and the Optimate Senators, the incident did little damage to his political career. Functioning in a populares capacity anyway, it likely had great benefit for him among the common people. Regardless, Caesar was quickly becoming a prime candidate for aggression from the Senate, and his role here may have played a part in later accusations during the Catalinarian Conspiracy.
Despite any personal grief over the loss of his wife, of who all accounts suggest he loved dearly; Caesar was set to remarry in 67 BC for political gain. This time, however, he chose an odd alliance. The granddaughter of Sulla, and daughter of Quintus Pompey, Pompeia was to be his next wife. Clearly aligned with the Senatorial optimates, perhaps Caesar was trying to deflect criticism from his treason trial. Regardless, his other actions had little to do with conservative policy and he continued his course of support for a populares policy. Now as a member of the Senate, thanks to his election earlier as Quaestor, Caesar supported the Lex Gabinia which was designed to grant Pompey the Great unlimited powers in dealing with Cilician Pirates. Later, and once again the face of bitter Optimate resistance, Caesar supported the Lex Manilia which eventually granted Pompey the unique and comprehensive command of the entire east against Mithridates. Obviously building a relationship with Rome's great general would play into his hands later, but the rivalry between Pompey and Caesar's benefactor Crassus, seemed to have little effect on Caesar. Despite this rivalry, Crassus continued to support Caesar's enormous debts over the course of the next few years.
Between the support of the two laws regarding Pompey's command, Caesar served as the curator of the Appian Way. The maintenance of this road, which stretched from Rome to Cumae and beyond to the heal of Italy's boot, was an important and high profile position. While it was enormously expensive on a personal basis, it gave a great deal of prestige to a young Senator, and Crassus' support certainly made it an achievable task for Caesar.
In 65 BC, Caesar, along with a young rival and member of the optimate faction by name of Bibulus, was elected as curule aedile. This magistrate position was the next step in the Roman cursus honorum and was a grand opportunity for the master of the public spectacle. The curule aediles were responsible for such public duties as the care of temples, maintenance of public buildings and perhaps most importantly, the staging of public games on state holidays. Caesar indebted himself to the point of near financial ruin during this time, but enhanced his image irreversibly with the common people. His games were spectacular affairs, and building projects during his term were ambitious. In one spectacle to honor his father, Caesar displayed 320 pairs of gladiators clad in silver armor which was an enormous expense. His co-aedile Bibulus was so unspectacular in comparison that he later commented in frustration that the entire year's aedile ship was credited to Caesar alone, instead of both.
Caesar pushed his agenda farther by erecting statues of Marius for public display. The senate, of course, was outraged, but Caesar's popularity made him nearly untouchable. They could, however, attempt to block his political path through other means. Caesar may have been nominated to take charge of quelling a disturbance in Egypt but was unable to win enough support to take the position. Even with this minor victory, the optimates wouldn't be satisfied though, as Caesar's brashness was a direct insult. His Senate enemies would look for any opportunity to stop his progress while Caesar, though, had plans of his own.