What went on in the young emperor’s mind in these days is not reported, but it is not difficult to imagine. This time it was not high-ranking senators in Rome who had plotted to take his life, as at the beginning of the year — but members of his innermost circle. Even his own sisters, the people who were undoubtedly closest to him personally, had joined in a conspiracy to assassinate him. The comparatively mild treatment they received probably points to the close relationship that once existed among the siblings. In view of what had occurred, Romans would certainly not have considered it an overreaction if both of them had been put to death — a step, incidentally, that would have prevented Nero from ever becoming emperor. In whom could the emperor place any trust from then on? That was the overriding question of the moment. Relatives — his uncle Claudius, for example — were out of the question, as his prohibition of new forms of honor for any members of the imperial family made abundantly clear. Could he trust senators? That was unthinkable after what had taken place earlier in the year.
In Rome, too, at the center of the Empire, the dramatic events led to a general sense of uncertainty. Legal proceedings were taken against individuals who could be shown to have had conspiratorial contacts with Caligula’s sisters or the men who had been executed. In addition to the consuls, who had already been removed from office, several aediles and praetors had to resign from office and stand trial. Many who had not taken part in the plot must have felt uneasy as well. The disclosure of the conspiracy appears to have launched a wave of denunciations, not unlike what had occurred under Tiberius. Thus, for example, we know from the biography of the later emperor Vespasian, who was a praetor at the time, that ambitious men of modest origins took advantage of the situation to display their loyalty to the emperor. This group included Vespasian himself, who made a motion in the Senate to leave the corpses of the conspirators executed in Rome unburied — a proposal not in the best of taste, but indicative of the atmosphere in that period.
The Senate voted an ovation for the emperor, just as it had done after the first conspiracy at the start of the year, and sent a legation to inform him of their action and to demonstrate their support. To lead the group, they chose none other than Claudius, the man who possessed the greatest dynastic prestige after the emperor himself since the banishment of Agrippina and Livilla, and who would in fact later succeed Caligula on the throne. The emperor was outraged. The Senate had violated his express prohibition against honoring members of his family when they put Claudius in charge of the mission. Caligula also seems to have feared further plots. He sent most of the legation back to Rome before it even reached him, because he believed their real purpose was to spy on him and wished to prevent them from having any contact with members of his personal or military retinue. Only a few chosen delegates were permitted to continue on and meet with him, including Claudius, whom Caligula allegedly humiliated and threatened after the mission arrived.
Given this volatile situation of fear and mutual distrust, Caligula must have decided first and foremost to stabilize the military, since in the end his position of power rested on the army. His sudden departure for Germania had upset the original plans for war. It was now the beginning of November, and the season alone made a military campaign on the right bank of the Rhine unfeasible. In addition, the Rhine legions were in such a miserable state that they would not have been capable of carrying out a rapid strike.
Caligula’s first measures were thus aimed at reorganizing the troops there. A large number of centurions — key officers in the Roman military forces — were discharged on the grounds of age and poor physical condition, and the customary payments on retirement were reduced. Several commanders of forces redeployed to Germany from other provinces of the Empire received dishonorable discharges because they had arrived on the scene too late. Evidently they were suspected of having held back intentionally, waiting to see if Gaetulicus’s uprising would succeed. Galba, on the other hand, who had not stinted with his active support, received a special commendation. As the new supreme commander he was charged with making the army of the upper Rhine fit for action again. He refused soldiers’ requests for leave, and re-accustomed them to military discipline by constant maneuvers and forced marches in which he took part himself. Suetonius cites a saying that circulated among the troops and reflected the new conditions: “Soldier, learn to play the soldier; ’tis Galba, not Gaetulicus” (Galba 6.2). On the lower Rhine near Cologne and Xanten, where four further legions were stationed, another military reorganization appears to have taken place about the same time. There Lucius Apronius was relieved of his command and replaced with Publius Gabinius Secundus. The families of Apronius and Gaetulicus were connected, and Apronius had been responsible for several catastrophic defeats in battles against Frisian tribes.
In his Life of Galba, Suetonius reports that during that autumn the new governor repelled “barbarians” who had advanced even into Gaul, and in the Life of Vespasian he writes that the later emperor, then a praetor, proposed in the Senate among other things that special games be held to mark the emperor’s victory over the tribes in Germania. Dio’s account states that the emperor had himself acclaimed imperator a number of times. Thus it is apparent that several military engagements occurred in the fall of the year 39 and ended successfully for the Romans. In his Life of Gaius Caligula, however, the same Suetonius relates some bizarre stories depicting the military actions carried out under the emperor’s command as pure farce. He reports, for example, that Caligula gave orders to some men from his Germanic bodyguard to cross the Rhine and hide there. Then he arranged for a report to be brought to him after breakfast with a great to-do that the enemy had arrived, and he rushed off with some friends and cavalrymen from the Praetorian Guard to a nearby wood, where they chopped down trees and dressed them up to look like trophies. In the evening the emperor returned by torchlight and rebuked the men who had stayed behind, calling them cowards; to the participants in his “victory,” however, he awarded a new kind of military decoration. Since Suetonius himself included passages in his biographies of other emperors about very serious military engagements on the upper Rhine, which were at least partly successful despite the condition of the troops, the story about the game of hide-and-seek can easily be recognized as a military exercise in which the emperor personally took part. Suetonius has taken the event out of context and distorted it.
Tacitus elsewhere briefly reports the vast scale of the preparations, but no extensive military action could be carried out before winter began. Caligula therefore left the front along the Rhine and spent the winter in Lyon, capital of the province of Gallia Lugdunensis, which at that time was also the site of the sole imperial mint for coining precious metals. Clearly tax assessments were calculated here in order to finance the huge war effort, as is reflected in Dio’s claim that the emperor had the tax rolls of Gaul brought to him and gave instructions for the richest inhabitants to be executed. It is doubtful, however, that he actually selected this particular way to raise revenue, for at the same time the emperor put his sisters’ entire sumptuous household effects up for auction, including their slaves and even freedmen. Since the auction was a great success, Caligula afterwards ordered much of the valuable inventory accumulated in other households of the imperial family during the reigns of Augustus and Tiberius to be sent from Rome and auctioned off as well. The shipments were reportedly so large that the government had to seize private vehicles; the transportation of grain to Rome was affected and there was a shortage of bread. Dio states that Caligula conducted the auctions personally, and that “the finest and most precious heirlooms of the monarchy” came under the hammer (Dio 59.21.5).