Your post and picture inspired me to do some reading
on Hadrian's Wall. A fascinating story about its building nearly 2000 years ago for still-unknown reasons, its preservation beginning in the 1830's, and its extent today.
The Roman Empire was spread far and wide. This northern wall was to "separate Rome from the barbarians" to the north, defeating them having proved more difficult than worth the effort. It says that or something similar most places we noted.
Well not according to the Wikipedia post I linked to above:
.... reasons for the construction of the wall vary, and no recording of an exact explanation survives....Scholars disagree over how much of a threat the inhabitants of northern Britain really presented and whether there was any economic advantage....[The Wall was] never expected to stop tribes from migrating or armies from invading, and while a frontier protected by a palisade or stone wall would help curb cattle-raiders and the incursions of other small groups, the economic viability of....a wall 72 miles long along a sparsely populated border to stop small-scale raiding is dubious....