On Nov. 6, 355, Roman Emperor Constantius II proclaimed his cousin Flavius Claudius Julianus, a 23-year-old student in Athens, Caesar of the western provinces. A few days later the ever-paranoid emperor married off Julian to his own sister Helena and assigned the young theosophist to the rebellious province of Gaul, perhaps hoping his potential rival would die there in battle. On December 1 Julian dutifully headed east to confront an invasion by a confederation of Germanic tribes known as the Alemanni.
In 356 Julian recovered Colonia Agrippina (present-day Cologne) from the Franks, only to be besieged by the Alemanni for several months southeast of Paris. When he mounted a two-pronged counterattack along the Rhine in 357, his column lost time chasing German raiders, while the larger second column fled under ambush by Alemanni forces and retired into winter quarters. Emboldened by intelligence that Julian had only 13,000 men, the Alemanni king, Chnodomar, gathered 35,000 German warriors on a hillside outside the ruined Roman fortress at Argentoratum (present-day Strasbourg) and openly defied the Caesar.
The Alemanni right, under Chnodomar’s nephew Serapio, lay concealed amid thick woods, ready to ambush the approaching Romans. Chnodomar anchored the left with his best cavalry, interspersed with foot soldiers assigned to bring down the Roman horses. The center comprised a mix of Germanic chieftains and their warriors. Julian arranged his infantry in two disciplined lines, with his cavalry on the right.
As the armies closed, an overconfident Chnodomar and fellow chieftains dismounted to lead their warriors into battle. The Roman left, under Julian’s deputy, Severus, detected Serapio’s concealed troops and was moving against the Alemanni center when Julian’s cavalry gave way. With the Roman cavalry out of the picture, Chnodomar charged Julian’s center.
While the Alemanni warriors were generally larger and stronger, the Romans had superior training and discipline and inflicted heavy casualties. Regardless, a shock force of Germans managed to breach the Roman line and force its way to the heart of Julian’s position. There his elite veterans ultimately prevailed, forming a tightening crescent around the exhausted Alemanni, whose pullback degenerated into a rout. Pursued to the banks of the Rhine, most of the Germans swam to safety, but Chnodomar himself fell captive, and Julian sent him to Constantius as a prize. The Romans claimed 243 men killed and estimated Alemanni losses at 6,000 slain in combat and 2,000 killed or drowned while seeking to swim the river.
Julian prudently did not cross the Rhine but instead campaigned to drive any remaining Germans from Gaul. His victory restored Roman control of the Rhine’s right bank and set the young commander on course to eventual coronation in Constantinople as the last non-Christian emperor of Rome.
Don’t cramp your own style. The Alemanni formed their line between the Rhine and heavy woods, restricting their maneuverability and neutralizing their numerical advantage.
Use good horse sense. By dismounting to lead their warriors into battle, Chnodomar and his chieftains ceded combat oversight and denied themselves a cavalry option.
Never underestimate an opponent. The Alemanni had already driven off superior Roman forces led by professional soldiers. They assumed that Julian, an inexperienced young intellectual, would be easy to defeat. He proved them wrong.
Quit while you’re ahead. Julian wisely held his pursuing Romans at the Rhine, as the forests beyond harbored waiting bands of hostile Germans and Franks.