Trajan Books

“...the legion, which as we have noted may already have been depleted by Trajan's troop movements, was moved north-westwards whole or in part from York to a new fortress at Carlisle sometime in the 110s to counter a growing threat from the south-west of Scotland. Then, at a date probably around 120, an uprising began in the Lowlands that gathered momentum and engulfed Trimontium at Newstead and the other forts further south along two corridors, one down Dere Street to the Corbridge area and the other veering south-west towards Carlisle. At some point, probably early in the rebellion, the IXth, accompanied by a large auxilliary force (scholars rarely mention that some auxilliary units from Britain are also unaccounted for after the 120s), emerged to engage a native force of superior numbers.

...it would be good to have more material evidence to confirm the Borderlands as the epicentre of the unpleasantness. Only time and the future assiduous efforts of another legion, this time of metal detectorists, are likely to tell us if the forlorn artefacts strewn across the moorlands of Lowland Scotland represent the last echoes of the IXth Hispana.”
― John H. Reid, The Eagle and the Bear: A New History of Roman Scotland