The Wall in Westeros was not only a physical barrier. As high as it was, it didn't keep out The Wildlings who were desperate enough. And there would never be enough men to guard every meter of it.
Built into the wall were protective powers against unnatural things and dark forces that most did not understand or even believe existed. In medieval times, phrases like "magic and wards" would have been used to describe what the wall contained.
I could imagine our wall might either have some bigger connection with advanced future tech, or with spiritual principles. Remember in the Bible, Satan was frustrated that he could not attack the man named Job, because God had a hedge of protection around Job and all his land.