I thought I'd take a look now at the likely make-up of the forces engaged in the initial battle of the 'Year of the Four Emperors' Campaign, namely the ambush at Locus Castorum.
For this I have been looking through the Histories of Tacitus which document the campaigns of AD69, and more particularly, the companion to the Histories written by Bernard W. Henderson, "Civil War and Rebellion in the Roman Empire AD69-70", which makes an effort to interpret the military aspects of the events described. Both of these are available to look at online; links follow at the end of this post.
As you might remember from a previous post:
the rather confusing ups and downs and ins and outs began with the fall of Nero and his replacement by Galba, only to see him in turn replaced by Otho; the Army in Germany, backing their own man, Vitellius, promptly set out to take on Otho.
We join the action as the Vitellan forces, split into two columns led by the Generals Caecina and Valens respectively, have entered Italy, and are approaching a showdown with the Othonians, who are made up of a column under Annius Gallus encamped at Bedriacum, and his back-up in the form of the main Army of Italy under Seutonius Paulinus and his deputy Marius Celsus.
The Vitellan troops were principally made up of the Army of Germany, along with a large number of auxiliaries of all types. Tacitus' text and his commentator Henderson point out the following:
Legio I Germanica
Legio V Alaudae
Legio XV Primigenia
Legio XVI Gallica
Legio IV Macedonica
Legio XXII Primigenia
Legio XXI Rapax
Legio I Italica
8 Batavian Cohorts which were originally formed as the auxiliaries of the Legio XIV Gemina, (which had declared conversely for Otho)
From the Garrison of Lugdunum, a cavalry 'squadron', (more correctly a corps) the Ala Tauriana
A corps of cavalry, the Ala Siliana, some 960 strong, which had deserted from the Othonian side
Gallic, Lusitanian and British auxiliary cohorts
Vexilia (detachments) of German troops (Likely native levies)
A corps of cavalry, the Ala Petriana
There are unfortunately no detailed entries as to the exact numbers of these troops, or indeed, how they were split up between the columns of Caecina and Valens, and furthermore, some losses had been incurred fighting Othonian forces in Narbonese Gaul on the way to Italy, and also at the city of Placentia, which Caecina had attempted to take by storm, as well as in a number of skirmishes with the enemy in the valley of the River Po.
Knowing exactly who was in Caecina's vanguard at Locus Castorum is rather difficult to pin down, certainly, Tacitus is at pains to point out that it was mainly formed by auxiliary troops operating in rough ground and a force of cavalry; these were re-inforced in somewhat piecemeal fashion from the entrenched camp at Cremona once the battle had begun.
The Othonian side, thankfully, was set out in some detail, and therefore is easier to describe, thus:
In the centre, three Praetorian Cohorts.
On the right, Legio I Germanica, with two auxiliary cohorts of foot and 500 cavalry.
On the left, 2,000 men of a Vexilia of Legio XIII Gemina, with four auxiliary cohorts of foot, and 500 cavalry.
In the rear, 1,000 cavalry under Celsus.
Again, the overall number is hard to define, given the unknown compliment of men available to Legio I; the Praetorian Cohorts were ostensibly 1,000 each.
It is likely that the opposition under Caecina had initially a smaller number of men in the ambush, but soon they were appearing in such numbers as to cause the Othonian commanders to break off the engagement, perhaps 12~14,000 in each force therefore might be about right.
The narrative of the engagement must be set against a background of the likely arrival of reinforcements for the Othonian side from the Army of the Danube, and the need for the Vitellans to dominate the strategically important road network in the area, as well as seek a victory in the face of the recent reverse at the walls of Placentia.
Caecina, therefore, wanted to take the initiative, and decided to set an ambush in the vicinity of Locus Castorum which would lure the Othonians to battle. Twelve Roman miles east of Cremona, the raised military road of the Postumian Way ran for a short distance through woods on both sides, and emerged from the trees to pass through an area of vineyards, which were thickly planted and criss-crossed by irrigation ditches, therefore making them difficult ground for formed bodies of troops.
Here, just before the road left cover, Caecina placed his auxiliary foot in ambuscade, and pushed his cavalry further along the road with the intention of employing a 'feigned flight' (Battle of Hastings 1066 style) that would draw on the Othonians.
Unfortunately for the Vitellan cause, however, his plan was betrayed to the other side, and Seutonius Paulinus set out with his troops in the order described above, intending to use his cavalry to envelop the enemy from either wing.
The onrush of the Vitellan cavalry was not reciprocated by the Othonians, and it appears that somewhat in frustration, or more likely due to poor command and control, the auxiliaries in ambush rushed from cover and fell on the enemies' horse. This move was countered by a pre-arranged order, which saw the cavalry withdraw through the ranks of their own oncoming infantry, with the impetuous Vitellans pinned in their front by the Praetorians, and Othonian auxilia of both horse and foot closing in on their flanks; a double envelopment was only prevented by the precipitate withdrawal of the would-be ambushers into the vineyards, which then became a great obstacle for Seutonius as he urged an advance - this was further tempered by the arrival of back-up on the enemy side along the road.
A developing encounter-style battle then , which eventually saw Caecina draw off back in the direction of Cremona, and Seutonius wisely not attempting to follow-up, given that he was already ten miles beyond his own entrenchments at Bedriacum, and would possibly meet the column of Valens who might arrive at any time to supplement Caecina.
Tacitus is rather hard in his summation on both commanders, for the apparent folly of Caecina for setting a weak and hasty ambush, and for the caution displayed by Seutonius; but this is tempered by the more militarily focussed Henderson, who sees the tactical benefits of both their approaches. As to how this might actually play out on the tabletop, I'm yet to find out, and worry that the weaker ambush forces might get pushed off table before any back-up might arrive; furthermore, I've realised that I need to paint up a lot more auxiliary troops and cavalry, too!
So, more to come on this in the future, and in the meantime, onward and upward....
Tacitus' text (with some enlargeable maps of the North of Italy):