His task there was to lead a campaign against the Germanic tribes east of the river, who had inflicted a major defeat on the Romans in the Teutoburg Forest a few years earlier. Germanicus’s wife, Agrippina, followed him, and soon afterwards their small son was sent north to join them, too. He thus spent his early years in a military camp. Supposedly it was Agrippina, known to take an active interest in military affairs, who hit on the idea of dressing little Gaius in a kind of miniature legionary’s uniform, as a form of flattery to the soldiers and designed to win their affection. He acquired his nickname, “Caligula,” from the little soldier’s boots he wore, and it stuck to him for his entire life.

Agrippina had anticipated the soldiers’ reaction correctly. The little boy became the favorite of the legions’ camp. After the death of Augustus, when the armies of the Rhine mounted a dangerous mutiny and tried to proclaim Germanicus emperor even against his will, the child is thought to have played a decisive role. When the precarious situation prompted the commander to send his wife and child to safety in Trier with their retinue, the solders are supposed to have become ashamed and called off the uprising. According to another source they took Caligula hostage to prevent his removal from the camp.

In early summer of the year 17 the family returned to Rome, where Germanicus was honored with a triumph for his campaigns against the Germanic tribes. Such a procession to celebrate a commander’s victories was the traditional apex of an aristocrat’s career, and a huge enhancement to his family’s prestige, but a goal achieved by very few. Germanicus’s triumph is said to have been staged with exceptional pomp. Trophies, prisoners, and depictions of the mountains, rivers, and battlefields were included, so that the Roman public could get a vivid picture of the popular general’s feats. Caligula, not quite five years old, and his four siblings stood at the center of the grand display with which the city celebrated Rome’s military success in the North and honored Germanicus: “To the spectators the effect was heightened by the noble figure of the commander himself,” writes Tacitus in his Annals, “and by the five children who loaded his chariot” (2.41.3).