A small section of the existing Hadrian's Wall at Peel Gap near Once Brewed, England.  Built starting in 122AD under the rule of Emperor Hadrian & spanning 73 miles from the Irish Sea to the North Sea, it served as a northern defensive fortification for the Roman province of Britannia until the end of Roman rule in 410AD.  The north side of the wall was also accompanied by a v-shaped trench for defense.  Today, much of the wall has disappeared except for here in the central hilly sector.  Originally 15-20 feet in height, the wall has been much reduced for later stone building or other nearby rock walls.  Pennine Way, a 268-mile long national trail in the UK, follows alongside the wall.

More info here: https://en.wikipedia.org/wiki/Hadrian%27s_Wall