It wasn't exactly built for that, though.
It was built to show the edge of the Roman Empire. Anybody was allowed to pass through the wall, except, of course, hostile armies.
In fact, the actual purpose of the wall is still under debate by historians across the world. They know it wasn't for defense, or to keep the Scots out, though it purpose seems to drift in between multiple possibilities.
Antonines Wall was then later built, that particular invasion wasn't exactly a failure, was it, Shadowman?
