Though the reign of Gaius 'Caligula' Caesar began with much promise, some early actions foretold of more uncommon behavior to come. Soon after his ascension Caligula showed signs of future 'madness' and Suetonius gives evidence even through a certainly embellished story:
'he (Caligula) devised a novel and unheard of kind of pageant; for he bridged the gap between Baiae and the mole at Puteoli, a distance of about thirty-six hundred paces, by bringing together merchant ships from all sides and anchoring them in a double line, after which a mound of earth was heaped upon them and fashioned in the manner of the Appian Way. Over this bridge he rode back and forth for two successive days. attended by the entire praetorian guard and a company of his friends in Gallic chariots.'
According to Suetonius the entire reason for this grand display was that an astrologer once said, "Gaius (Caligula) had no more chance of becoming emperor than of riding about over the gulf of Baiae with horses."
Within 6 months of his rise to the highest power in Rome, Caligula fell very ill. The entire empire fretted over his well being, but the cause for concern was to prove to be misplaced. When Caligula recovered he returned as a changed man. The ancient sources blame the illness, which has been suggested in possible relation to epilepsy (perhaps passed down from Caesar) or even a genetic disorder from intensive familial inbreeding. However, while Caligula certainly could've been 'deranged' it's far more likely that his later behavior was a symptom of his environment than an actual disorder. He was simply the first 'emperor' to understand the absoluteness of his rule and the freedom to do with it as he pleased. A child reared in a world of violence, corruption and intrigue, one could hardly expect much more from the grown man.
Regardless of the reasoning, whether mental instability or true viciousness, after the illness all sources attest to a change in Caligula's behavior. An initial act upon recovery from his illness demanded that any person who had offered their life to the gods in sacrifice if, 'Gaius' would recover, should fulfill that obligation. He killed the former Praetorian Prefect Macro, his father in law and Tiberius Gemellus, his supposed heir. In a strange twist, during his illness, Caligula had named his sister Drusilla as heir, not only indicating the great affection he held for his sisters, but fueling rumors of wild incest. In AD 38 the oath of loyalty to the emperor also required the same oath be said to his sisters.
Tyrannical behavior continued and became increasingly cruel. Comments that he could easily order the death of magistrates, or slit the throats of lovers were common. The treason trials of Tiberius were re-instituted and one never knew what reason Caligula would find to confiscate their properties or lives. Caligula is attested to having said 'Would that the Roman people had but one neck!' Though this reeks of propaganda, it can certainly show an environment of fear that must have existed. Sexual depravity and escapades of all sorts were reportedly taking place. In addition to rumored incestual affairs with his sisters and stealing men's wives for his own pleasure, Caligula had been married 4 times, 3 of which took place during his short reign.
The strange and lewd behavior continued into the form of megalomania. An altar was built to honor himself as a living god. His favorite sister Drusilla, who died suddenly in AD 38, was deified as a member of the slowly growing imperial cult. Statues of the emperor were ordered to be erected all over the empire and in Jewish synagogues, with clear ramifications of civil disorder.
It was suggested that he opened a brothel right inside the imperial palace and that his favorite horse was kept in an ivory carved stable within the palace walls as well. Dinner parties were arranged in the horse's honor, and though of doubtful truth, it was even recorded that Caligula considered making it a Consul. Expenditures were out of control, and the entire imperial treasury, carefully built up by Tiberius, was squandered in Caligula's excessiveness. Gem laden ships and monumental villas were built for no other reason than to satisfy the whims of the Emperor.
Not only was the aristocracy of Rome at danger by virtue of close association to their 'leading citizen' but his spending threatened the security of the empire itself. To offset it, he introduced new heavy taxation, including taxes on prostitution that simply burdened the population as a whole. In just a few short years, Caligula went from being the people's great savior to another despised despot. What was worse, thanks to his laughable military campaigns to come, he was in danger of losing the loyalty of the legions.