Battle of Strasbourg - Roman Order of Battle

Roman Order of Battle

The composition of Julian's army at Strasbourg can only be partially reconstructed. Ammianus gives the names of only five regiments in his account of the battle itself. But at other points of Ammianus' narrative of Julian's campaigns in Gaul, and also in Zosimus' history, there are mentions of other regiments in his comitatus, which were very likely at Strasbourg also.

A comitatus at this time probably contained only three types of regiment, all of them of the top, palatini, grade: cavalry vexillationes and infantry legiones and auxilia. There is much uncertainty about the size of late Roman army units. The official strength of vexillationes and legiones seems to have been 800 and 1,200 respectively. But actual strengths recorded were 400 and 800 respectively. A midpoint between these figures is assumed here of 500 for vexillationes and 1,000 for legiones palatinae. The strength of the auxilia palatina regiments is disputed. They may have been as large as legions, or only half the size. Half the size is more likely, as it accords best with the available evidence. Also, if an auxilium was the same size as a legion, there would seem little purpose in the distinction between the two types of unit.

The sources give the following units for Julian's comitatus:

The Ioviani and Herculiani legions and equites Dalmatae are not mentioned by the sources as under Julian, but as part of the Gaul comitatus of usurper Magnentius. They are likely to have been inherited by Julian. If all these units were present at Strasbourg, the infantry total is 1,500 short, or 3,500 if Severus commanded an extra 2,000 men. Probably the names of a number of auxilia regiments (and possibly a legion) are missing in our sources. If so, at least one of these units is likely to be a sagittarii (archer) unit, as a comitatus would be incomplete without archer capacity. Overall, the most likely scenario is that Julian's force at Strasbourg consisted of 5-6 legiones and 10-14 auxilia of infantry and 6 vexillationes of cavalry.

As regards cavalry, Ammianus mentions only cataphracti in his account of the battle. But it is virtually certain that they were only part of his force. In the late army as a whole, only 15% of cavalry regiments were heavily armoured cataphracti. These were suitable for the shock charge. Two tribuni (regimental commanders) of cataphracts were reported killed at Strasbourg. There were thus at least two vexillationes of cataphracts (1,000 horse) engaged. Elsewhere in Ammianus and Zosimus it is stated that Julian had a regiment of Gentiles and a regiment of scutarii under his command. Both these were normal (semi-armoured) units that represented the majority (61%) of the late army's cavalry and were best suited to mêlée combat. There is also mention of light (unarmoured) units of equites Dalmatae (javelineers) and equites sagittarii (mounted archers). Light cavalry was used for harassment and pursuit. The likeliest scenario is that all these were present at Strasbourg, with two vexillationes each of heavy, normal and light cavalry engaged. It is thus likely that cataphracts were about a third of Julian's cavalry at Strasbourg, an unusually high proportion. In addition, Julian had his personal escort of 200 picked cavalry. These were probably a detachment from one of Constantius' scholae (elite cavalry squadrons, believed 500-strong, that served as the imperial horse guard).

As regards the line of battle, we are given a little information by Ammianus. He reports that the right flanks of each line, front and reserve, were held by two auxilia regiments and the centre of the reserve line was held by the Primani legion. A possible order of battle that fits the available evidence is shown in the diagram of the battle.