As for Caligula’s share in his Augustan Principate, all that can be said is that he played the role to perfection. Though indubitably better than before his elevation to the throne, his situation continued to be anything but simple. The two manipulators who had made him emperor had cemented their own positions of power at the same time and were hardly about to give them up voluntarily. Furthermore by adopting Gemellus he had created an abiding rival for the throne. Thus the two powerful men behind the throne always had an option open; there was an alternative to Caligula.
As in other pre-modern monarchies, the advent of a new ruler in ancient Rome frequently bred conflict at the center of power — structural conflict, intensified through generational differences. Would the trusted entourage of the old emperor adjust to the new one? They owed their rise and influence to the old ruler and had not been chosen by the new one; their position was independent of his favor, at least in the beginning. Typically a new ruler gathered his own close confidants around him; these began as rivals of the inner circle from the old regime and then pushed them aside. The rearrangement could be an adaptation, or it could be a great upheaval.
Caligula’s closest confidants were his sisters — who shared with him not only ties of blood but also the experience of great danger under Tiberius; the husband of one of them also belonged to the inner circle. Caligula felt extraordinary affection for Drusilla especially. Tiberius had arranged her marriage to Lucius Cassius Longinus, but they were now divorced; her second husband, Marcus Aemilius Lepidus, belonged to the same generation as the siblings. Lepidus came from a high-ranking family with its own ties to the imperial house, and he was Caligula’s closest confidant among the aristocracy. What kind of relationship would develop between this circle on the one hand and Macro and Silanus on the other?
A resolution developed more quickly than might have been expected. In the eighth month of his reign, at the end of October 37, Caligula fell gravely ill. No information has survived about what the disease was. The population of Rome was alarmed and grieved. Large crowds are said to have demonstrated their concern for the young emperor by surrounding the Palatine Hill every night, waiting for news. What would happen if he died? Who would succeed him?
All the known events of the next few weeks allow the following conclusion to be drawn: Macro and Silanus, the two leading men, seized the initiative. In case Caligula should die, they conferred with a number of people and prepared the way for Tiberius Gemellus, the only possible successor in the existing dynastic constellation. This was the only rational strategy, the only one that fit the circumstances, although they obviously set about implementing it a little too soon. Any other choice would have encouraged the ambitions of aristocratic pretenders to the throne and risked an outbreak of violent conflict. A crisis had developed sooner than anyone could have anticipated. Caligula’s adoption of Gemellus had been strategic, but laden with possible future difficulties. It would constitute a problem if he were to have a biological son or wish to name someone else as heir. In the meantime, however, there was no alternative to Gemellus, and this meant that if Caligula died, his sisters and Aemilius Lepidus would lose their unique position and the power attached to it; conceivably even their personal safety might be threatened.
In this situation Caligula first seized the initiative as emperor. From his sickbed he named his favorite sister, Drusilla, to inherit the imperial “property and the throne” (bonorum atque imperii; Suet. Cal. 24.1), in effect making Lepidus his successor. As soon as he regained his health, he laid a plan that was brutal but under the circumstances only logicaclass="underline" to eliminate Tiberius Gemellus, who as long as he lived would remain a magnet for conspirators hostile to the emperor and ambitious to place their own man on the throne. Gemellus was accused of plotting against Caligula, of having counted on his death and attempted to profit from it. A centurion and a military tribune were dispatched and forced him to commit suicide. Philo vividly describes the tragic scene: Since Gemellus had no experience of warfare and had never witnessed a suicide, he had to be instructed in the technique, “and having received this first and last lesson he was forced to become his own murderer” (Phil. Leg. 31).
The loss of an established candidate for the succession weakened Macro and Silanus. Not long afterward, probably at the start of the year 38, it was the turn of Macro and his wife, Ennia, to fall from power. To replace a Praetorian prefect was an enterprise fraught with danger, but nevertheless it was achieved smoothly in two steps. First the emperor appointed Macro prefect of Egypt, the second-highest office in the Empire for a knight, and replaced him not with one man but with two. Caligula was following Augustus’s modeclass="underline" Since the man in charge of the emperor’s bodyguard always represented a potential threat, Augustus had named two to the position at a time, ensuring that they would be rivals for power and keep an eye on one another. Caligula seems to have chosen the appointees wisely. They were men plucked from obscurity (only one, Marcus Arrecinus Clemens, is known by name) and owed a particularly great debt to the emperor as a result.
Before Macro could embark for Egypt, he and many other people were charged with crimes and then either executed or forced to commit suicide. In Philo’s words, Caligula began to “fabricate charges against him, which though false were plausible and readily believed”; on one count Macro had supposedly claimed that Caligula was a creature of his making and that the emperor owed the throne to him (Phil. Leg. 57–58). Some were found guilty on the basis of witnesses’ testimony and the evidence from earlier trials, supposedly destroyed, that they had participated in attacks on Caligula’s mother, his brothers, and their supporters. Others were accused of behaving inappropriately during the emperor’s illness. The charges suggest that the main targets were old enemies of Germanicus’s family who had hoped for Gemellus’s accession and presumably acted accordingly. One such man was Avillius Flaccus, who lost his office as prefect of Egypt in the autumn of 38.
Then it was Silanus’s turn. It sufficed for the emperor to indicate his displeasure with him in the Senate. Caligula altered the procedure so that the former consuls would vote in order of seniority, thus terminating Silanus’s privilege as highest-ranking senator. Everyone who had lived through the reign of Tiberius realized that it was only a matter of time until some unscrupulous senators would bring charges against the man whom Caligula had publicly demoted. Silanus saw the handwriting on the wall and committed suicide, enabling his family to retain his fortune, since if he had been tried and found guilty it would have been confiscated.
Judged by the standards of a modern society in which political disagreements and power struggles are conducted without violence, Caligula’s elimination of the people who had helped him secure the throne, and particularly his treatment of young Gemellus, were reprehensible. Given his experience of life near the throne, however, he may well have felt he had a stark alternative: Either them or me and my family. From the perspective of today this assessment can hardly be termed incorrect, and contemporaries concurred with it. Philo, whose aim is otherwise to stress Caligula’s immorality, cites at length opinions that ran counter to his own appraisaclass="underline"