When it comes to the wall I think you have to look at it in a number of ways and in the historical context,
1/. It was a defensive wall and did have success in stopping the raids and controlling the extreme North of the Roman Empire. It was just not about the stone wall, there was the Vallum comprises a ditch, nominally 6 metres (20 ft) wide and 3 metres (10 ft) deep, with a flat bottom, flanked by two mounds about 6 metres wide and 2 metres (7 ft) high. When you stood and look North from the wall the horizon was cut back and build up so soldiers on the wall had a clear view of things moving a number of miles away from the wall.
2/. The Roman expansion was as much about trade and the economy than it was about military might, sure the Emperor needed success to keep the masses happy. But by building the wall and limiting the ways through that wall it was possible to tax the traders and control the goods.
3/. The wall was a statement to British tribes, it was a physical way of we are here and we are here to stay. I think there is a lack of realisation just how long the Romans were in Britain, arrived in AD43 and left around AD410. That is 367 years, so if the Romans left Britain in 2018 it would mean they arrive in 1651. The year the English Civil war ended and over 125 years before the US independent declaration. The British tribes were living in small communities and it is hard for us to imagine the impact of the wall and the other buildings] would have had, it just showed the shear might of the Romans. On that can you imagine what it would have been like to go to battle against the Romans and then see an Elephant……………. the next time they appeared was about 1100 years later.
My retirement [or semi-retirement] comes up in 3 to 5 years and I am thinking of a new career, buying a house with land to stay a Glamping campsite or holiday accommodation. Hadrian’s Wall is running second in my thinking, first is Normandy, but Hadrian is running a close second.
Walls are popular, ask the Orange one?
On the Great wall of China I once heard someone say the wall stretches for 13,170.696 miles and not a single ATM in it anywhere!