It's on the Antonine Wall that was built 100 miles north of Hadrian's Wall in 142AD and ran between Glasgow and Edinburgh. I'd never heard of it I have to admit and certainly not spoken of much it would seem (not down this neck if the woods anyway!!).
One other thing...I've only just realised (doh) that Ben Robinson with the drone (that someone else seems to operate) was the guy who was the Flying Archaeologist in that other terrific series.