March, 37 CE: At about 25 years old, Caligula was named Rome's third emperor, the first direct descendant of Augustus to take the throne (click here for a coin on which Caligula emphasizes this relationship). The reign began with good feelings all around, since Caligula declared an amnesty for all Romans imprisoned or exiled under Tiberius, posthumously restored honor to his mother and brothers, and stopped the treason trials, getting rid of the informers in the process. One month after his accession, his grandmother, Antonia, died.
October, 37 CE: Caligula fell seriously ill, with what was described at the time as a “brain fever”; there was great mourning in Rome, and much joy at his recovery. There were a number of freedmen in his close circle who attained considerable influence: Helicon, his chamberlain; Apelles, a tragic actor; and most wealthy and powerful of all, Callistus, a kind of imperial secretary.
38 CE: Early in the year, Caligula forced his father-in-law, Gaius Silanus, and young Gemellus, grandson of Tiberius, to commit suicide by accusing them of treasonable activities. Although the prefect of the Praetorian Guard, Macro, had been influential in helping Caligula secure the throne, the emperor apparently felt that Macro was becoming too powerful. Caligula tricked Macro into believing that he was being made prefect of Egypt and then had him arrested and executed. Later in the year Caligula's favorite sister, Drusilla, died; he had been so close to her that there were rumors of incest. In the manner of the eastern monarchs, Caligula had Drusilla deified; she was the first Roman woman ever officially declared a deity, but her divinity did not survive his reign because he had so egregiously flouted Roman precedent (in contrast, when Claudius had Livia deified, he emphasized her role as “diva Augusta,” wife and mother of emperors). Caligula also minted coins in Drusilla's honor (scroll down on this page to see a coin featuring the three sisters of Caligula).