Ludwig Quidde, who made this term famous at the end of the nineteenth century, describes this “disease” as “megalomania, carried to the point of regarding oneself as divine; disregard for all limits of law and all the rights of other individuals; brutal cruelty without purpose or reason.” Although these elements are also found “in other mentally ill people,” the unique quality of an emperor’s madness lay in his position as ruler, which “provides particularly fertile soil for the seeds of such a predisposition and permits them to develop unhindered in a manner that is otherwise hardly possible.” For Quidde’s contemporaries, however, this brief biographical sketch of Caligula had a double meaning, a hidden intention beneath the surface of the words. They saw the depiction as so clearly aimed simultaneously at another emperor, Kaiser Wilhelm II of Germany — who was certainly not insane — that Quidde’s book ran through thirty printings within a short time. It also earned the author three months in prison and ended his academic career. Yet these events did not weaken the impact of his conclusions about Caligula. The author of a recent biography (published in 1991) still describes the emperor as “crazy,” and a recent survey of the scholarly literature contains references to his “imperial madness.”

Readers of this biography of Caligula thus appear to be in for quite a story — and indeed they are. Matters are considerably more complicated than might appear at first glance, however. It was established during the nineteenth century that ancient accounts of this emperor are by no means as much in agreement as they may seem. Take Caligula’s sex life, for example: The claim that the emperor committed incest with his three sisters is misinformation that surfaces for the first time in Suetonius. Its hollowness is easily proved: The emperor’s two contemporaries Seneca and Philo, who were both familiar with aristocratic circles in Rome and well informed, heap invective on the emperor and would hardly have failed to mention such a charge had it been in circulation then.