Courtesy Simon Elliott's SEPTIMIUS SEVERUS IN SCOTLAND, p. 12
For years now I hav insisted that L. Artorius Castus' three British legions were detachments (for an example of my thinking on this issue, see https://mistshadows.blogspot.com/2023/12/implied-vexillations-in-roman.html). This was based on the belief among mainstream Roman scholars that he had taken this force as dux outside of the province. We had only two possible choices for the ARM[...]S lacuna on the Castus memorial stone: ARMENIOS and ARMORICOS (which I was the first person to show would fit on the stone with allowable ligatures).
But if we instead allow for ARM[...]S representing ARM(ATAS) GENTES, 'armed tribes', then we can confine Castus' dux mission to Britain itself. And when we do that, the situation with the British legionary force changes completely.
I've already posted a passage from Simon Elliott's book SEPTIMIUS SEVERUS IN SCOTLAND on another blog, but will provide that again here for context:
Adding to this (from pp. 146-147 of the same volume), a description of the entire force assembled for the Northern campaign:
The reader will notice the presence of all three legions.
In my defense, I had commented several times that had Castus led legionary troops north, as prefect of the Sixth he most certainly would have taken his own legion practically entire, along with generous detachments from the other two legions.
But given Elliott's hypothetical reconstruction, I thought to ask Professor Roger Tomlin (who himself prefers the Armenia reading for the Castus stone) the following question:
"Is it realistic for all 3 British legions to have been taken North by Severus, allowing for skeleton garrisons having been left to man the three legionary forts?"
His response?
Tomlin:
"We don't know whether Castus was appointed with ius gladii or if this was added later – another reason for supposing that his appointment was in response to a special need / crisis. If he were simply being rewarded for good service, then it is more likely that he would have been given the next good job going, rather than having one created simply to reward him.
As for Severus in Britain, it is likely that, as in the Wall-building in the previous century, all three legions would have been mobilised."
CONCLUSION:
If we wish to interpret Castus' dux mission as his commanding three entire legions, rather than assume he was implying legionary vexillations, and we except both the date range of the stone and the emergency nature of the Liburnian procuratorship, then we must conclude that Castus participated in the British campaign of Severus and was made governor of Liburnia by Caracalla.
