The correct answer is - d. the wall marked the northern defensive boundary of Roman Britain.
The Hadrian wall was built under the rule of the Emperor Hadrian, after whom it got its name. The Roman emperor ordered the building of this wall because of the Pictish tribes from Scotland, which were constantly entering the northern parts of the territory of Roman Britain and were robbing the people. The purpose of the wall was to be a defensive line against the Picts, and in general, it did its job very nicely, keeping the Picts north of it.
