All the ancient histories are meagre, universally hostile and largely sensational in their accounts of Gaius. This has resulted in many of the events of his reign remaining unclear and it is impossible to get an idea of the true nature of Gaius.

Gaius was born in AD12; he was the third child of Germanicus, Tiberius’ adopted son and Agrippina the elder, the daughter of Julia and Agrippa. As a baby he was prone to epileptic fits and when he accompanied his parents to Germany, on Germanicus's appointment there as a general, Augustus was concerned enough to send two doctors to look after him. His nickname Caligula comes from this time as Agrippina would dress him in a miniature soldier’s uniform which boots were called caliga and Caligula literally means little boot.

Gaius's early life was very difficult, in AD19 Germanicus died while in Syria, accusing Calpurnicus Piso of poisoning him, his mother Agrippina believed the accusations and also the rumour that Tiberius was involved, causing her to lead a crusade against Tiberius. The relationship between Tiberius and Agrippina deteriorated quickly and she became a rallying point for those who did not approve of Tiberius.

In AD27 Gaius was sent to live with his great-grandmother Livia, following her death in AD29 he was transferred to the care of his grandmother Antonia. In Antonia's household he lived with three Thracian princes and Ptolemy, the heir to the throne of Mauretania, and it has been suggested that from this time he might have gained an absolutist concept of monarchy.

 In AD29 Agrippina and her sons Drusus and Nero were arrested on Tiberius orders, they were exiled and Agrippina died in exile in AD33, Drusus of starvation in AD29 and Nero in prison in AD29. During this period the Praetorian Prefect, Sejanus was at the height of his power and Gaius would have probably suffered a similar fate if he had not been summoned to Capri by Tiberius in AD31. Gaius remained in Capri until his accession in AD37, the only position of administrative responsibility Gaius held was an honorary quaestorship in AD33.

Accession

When Tiberius died on 16 March AD37 he left his estates to Caligula and Tiberius Gemellus as joint heirs (it was not the Roman system to have any ability to leave the Principate to either boy, they were simply left Tiberius’ estate), their only claim to the Principate was this legacy and being of the Julio-Claudian family. Macro, the Praetorian Prefect, had the will declared null and void on grounds of Tiberius’ mental instability in giving the authority to a mere boy (Tiberius Gemellus) to rule, this was done more because a reason had to given rather then as a slight to either Tiberius. Macro, who had bought over the Praetorian Guard and the army commanders, backed Gaius and if the senate realised they had no real choice in the matter is unknown as the senate enthusiastically agreed on their choice. The senate may have agreed because of a belief of Gaius being like his father or perhaps the senate hoped that Gaius’ youth would make him easily manipulated. It is noteworthy that this process suggests that the heir of the Princeps was in some way designated as the next Princeps. It is likely that a number of senators would have been unhappy giving power to an untrained 25 year old and Gaius tried to sooth these people by playing on the sympathy felt for him due to the death of his parents and by placing himself under the senators guardianship, offering to share his power with them in a very Augustan fashion.

Gaius arrived in Rome in a stately procession from Misenium, the people greeted him with gladness and thanksgiving, calling him by pet names like ‘star’, ‘chick’ and ‘baby’ and sacrifices were made along the course of his route. Gaius arrived in Rome on the 28^th of March and the senate bestowed on him ‘power and authority over all things’. This bestowed on Gaius the tribunicia potestas and proconsular imperium and the other associated titles that Augustus had held in one block. This was very different then Augustus’ gradual accumulation of power and effectively ended the discreet use of power of the monarchy Augustus had crafted and Tiberius had tried to maintain. Caligula seemed to view the Principate as a monarchy, perhaps because his age and lack of experience made him feel vulnerable. His claim that he had ‘every power over every person’ was seen as a sign of madness by the ancient sources did in fact have a good constitution basis and is a reflection of Caligula’s view of his powers.