Battle of Strasbourg - Prelude

Prelude

As reinforcement for the Gaul comitatus, Constantius provided Julian with a cavalry escort consisting of 200 scholares, a regiment of cataphractarii (heavily armoured cavalry) and some mounted archers (total about 1,200 men). En route to Gaul from Milan, at Taurini (Turin), he received the calamitous news that Cologne had fallen to the Franks. He spent the winter of 355/356 with his escorting troops at Vienna (Vienne), not far South of Lugdunum (Lyons). For the 356 campaigning season, Julian's first task was to link up with the main Gaul comitatus, which had wintered at Remi (Rheims) under the command of the magister equitum, Ursicinus' recently-appointed successor, Marcellus. This involved a long march through country swarming with Alamanni raiding bands, many of which were as large as Julian's own escort and expert at ambuscades. On the way, Julian surprised and drove off a large barbarian force that was besieging Augustodunum (Autun) and defeated a raiding band in the Morvan wilderness.

At Rheims, Julian showed his characteristic boldness by deciding, in conference with his senior commanders, to deal with the Alamanni problem at source by marching straight to Alsace and restoring Roman control of the region. At Decem Pagi (Dieuze), however, his army was ambushed and nearly destroyed by a large German band who fell on two rearguard legions which had lost contact with the rest of the column in dense mist. They were rescued by auxilia palatina regiments that heard the uproar. Proceeding to Brotomagus (Brumath) in Alsace, Julian's army routed another German band in the field. But, after assessing the situation in Alsace, Julian evidently decided that his force was insufficient to prevail over the Alamanni alone. Instead, he set out to recover the critical lower Rhine city of Cologne. From Metz, he led his army via Treviri (Trier) to Roman-held Coblenz and thence along the Rhine to Cologne. Entering the ruined city unopposed, Julian's men were set to work to rebuild the city walls. Julian then concluded a peace treaty with the Franks. This had the important effect of removing half the opposition from the equation and allowing Julian to focus his resources on dealing with the Alamanni.

For the winter of 356/7, he chose Senones (Sens) near Paris as his own base, but quartered most of his troops in other towns, including the main body at Rheims under Marcellus, to spread the burden. A large band of Alamanni heard of his reduced escort, however, and besieged him at Sens. Julian's forces were able to hold out until, after a month, the Germans withdrew. He was so outnumbered by the enemy, however, that he was unable to sally forth and give chase. During the siege, Marcellus had failed to come to his assistance. For this omission, denounced as cowardice by Ammianus, Marcellus was dismissed as magister equitum by Constantius and replaced by Severus, a distinguished officer who was more compatible with Julian.

For the 357 campaign season, a plan was laid down at Constantius' headquarters in Mediolanum (Milan) to trap the Alamanni in eastern Gaul in a pincer movement. Julian would advance eastward from Rheims, while the major part of Constantius' comitatus in Italy (25,000 strong) was despatched under magister peditum (field marshal) Barbatio to Augusta Rauracorum (Augst) in Raetia, from which he was to advance northward to meet Julian. The Alamanni bands would be cornered and destroyed in the southern part of Germania I province (Alsace).

But large bands of Alamanni, ignoring the threat posed by the Roman manoeuvre, invaded and ravaged the rich Rhone valley, even trying to take the major city of Lugdunum (Lyon) by assault. The attack was repulsed as the walls of the city proved too strong and the garrison, presumably limitanei troops, too valorous. Nevertheless, the Germans had devastated a large area and taken vast amounts of booty.

However, the Germans were now trapped in the interior of Gaul with their way back to the Rhine barred by the Roman armies. In Julian's sector, the Caesar despatched squadrons of cavalry to lie in ambush on three roads and these successfully intercepted and destroyed the returning barbarian bands. But in Barbatio's sector, the main body of Germans were allowed to pass unmolested. Barbatio's chief-of-staff Cella rejected the urgent request of two of his cavalry tribuni (regimental commanders) Valentinianus (later emperor Valentinian I 364-5) and Bainobaudes to deploy their squadrons on a highway that they expected the enemy would use. The escaping force reached some islands in the Rhine near Strasbourg where the raiding-bands had moved their camps for safety in response to the Roman pincer movement. Nevertheless, Julian pursued them vigorously. Although without boats, his men succeeded in reaching one island, as the river had become fordable at some points due to summer drought. An entire raiding-band was surprised and slaughtered, a success repeated on a few other islands. In response, the Germans evacuated the remaining islands, removing their sutlers, baggage and booty to the far side of the Rhine.

Julian now turned his attention to rebuilding the fortress at Saverne, which had been destroyed by the Alamanni. Saverne lay astride the Mediomatrici (Metz) - Strasbourg Roman highway, at the mouth of the main entry route through the Vosges mountains into northern Alsace, a location with commanding heights overlooking the Rhine valley. While this work was proceeding, at some distance (probably in the vicinity of Strasbourg), the vanguard of Barbatio's army was attacked by surprise by a large barbarian force as it approached the camp of Julian's deputy, Severus, who was apparently operating separately from Julian. The vanguard fled in disarray, and instead of fighting, the rest of Barbatio's force disengaged and hastily retreated, closely pursued, out of Alsace and a good way into Raetia, losing most of their sutlers, pack animals and baggage. At this point, Barbatio, whose cooperation with Julian had been grudging at best, withdrew his army from the theatre of operations altogether, without Julian's permission. He sent his forces across the Alps into winter quarters in Italy, despite it being the middle of the campaigning season and the Alamanni being far from defeated or ejected from Alsace. This reduced Roman forces in Alsace by two-thirds and effectively sabotaged the pincer strategy. Ammianus states that it was unknown whether Constantius was behind Barbatio's actions, but it seems unlikely that the magister would have risked ceasing operations unless confident of the emperor's approval.

At this time, the Alamanni confederation appears to have been under the leadership of two kings, Chnodomar and Westralp. Chnodomar was the driving force. A man of prodigious stature, strength and energy, he was nicknamed Gigas ("the Giant") by the Romans. He was a formidable sight in his "flashing" helmet (probably gold-leafed) and full parade armour. He is described by Ammianus as the "evil mastermind" behind the invasion of Gaul.

Chnodomar could not ignore Julian's fortification of Saverne, as it threatened his control of Alsace and blocked his main access route into the interior of Gaul. He had come to see this region as Alamanni territory by right of conquest after occupying it for several years. He also claimed to possess letters from Constantius granting the Alamanni the right to occupy those lands. Chnodomar had been surprised and dismayed by Julian's successful campaigns of 355-7. But he was encouraged by his own success against Barbatio and the intelligence brought to him by a deserter that Barbatio's withdrawal had left the Caesar with only 13,000 men. Having driven two Roman magistri from the field (Barbatio and before him, Magnentius' lieutenant, Decentius), Chnodomar had lost the barbarians' traditional fear of pitched battles with the Romans.

The Alamanni high kings now ordered a mass mobilisation of all the confederation's member tribes, gathering their bands at Strasbourg. In addition, they received the timely support of the two Alamanni tribes near Raetia that had been pacified by Constantius in 355. Their leaders were overthrown in an anti-Roman coup by their optimates. Gundomad was slain and Wadomar forced to break his treaty and lead his warriors to join Chnodomar. Finally, they summoned the assistance of certain non-Alamanni tribes (probably Burgundians), partly for services rendered in the past, partly for payment. At Strasbourg on the Rhine (about 32 km SE of Saverne), they gathered a combined force of some 35,000 men, according to Ammianus. This figure may be an exaggeration, but the exceptional size of the levy is shown by the presence of all the Alamanni kings and the report that German bands were crossing the Rhine to Strasbourg continuously for three days and nights. Their aim was to bring Julian to battle and crush him by sheer weight of numbers. They provoked Julian by sending him an ultimatum to evacuate Alsace immediately.

Julian was now faced with a finely-balanced judgement call. The safer option was to ignore Chnodomar's challenge and to keep his forces in their fortified bases and request and await reinforcements, if necessary until the following year's campaign season. But the performance of Barbatio and the imperial comitatus in the recent campaign cast doubt on whether such reinforcements would be supplied and on their value if they were. Such a course would also expose Gaul to a massive Germanic invasion just when the harvest was due. Alternatively, he could fight Chnodomar alone. This offered the prospect of a decisive victory, since the Alamanni forces were now, unusually, concentrated and not divided into many disparate bands. This argument was strongly made by Florentius, the praefectus praetorio Galliarum (governor-general of Gaul), who had the crucial job of ensuring the army's supplies. The Romans almost always won pitched battles with barbarians, because of their superior equipment, organisation and training. But in this case it was clearly a high-risk option because of the Germans' massive superiority in numbers. Nevertheless, Julian decided to give battle.