When I went to school, the only wall we really learned about was Hadrian's. It was, we were taught, a barrier to protect the edge of the Roman empire from those outwith it; that is, the bad guys to the north with aggressive intent. The word barbarian was probably used.
But, according to Rory Stewart in The Marches, that is no longer the right answer according to the satraps who order history curriculum matters in Scotland. They have decreed (it's a MacFatwa) that the wall was only a base for patrols and for the army to stop small-scale raids, slow down big raids, stop smuggling, and keep the troops busy building and repairing it. "There is no debate", they pronounce in their rigid, ideological revisionist history.
Woe betide, then, the clever Scots student who writes a brilliant essay full of wit and wisdom arguing, on the balance of possibilities, the opposite view. Zero marks will be forthcoming, and maybe worse.