Why I am building Castle Black and how it is related to Hadrian's Wall

I have a great interest in the Classical world and all it's inner workings and because of this, I have chosen to build my own interpretation of Castle Black, located at the very Northern edge of the claimed lands of Westeros in Game Of Thrones, and am comparing it to the likes of Hadrian's Wall, located in Northern England, from the banks of the River Tyne near the North Sea to the Solway Firth on the Irish Sea.

Hadrian's Wall was a defensive fortification build by the Roman Empire to keep out invaders to the Roman providence of Britannia. It also stood as the Northern most border of the Roman Empire's reach. It's construction began in 122 AD in the reign of the emperor Hadrian (hence the Wall's name). It had a stone base and a stone wall and there were mile-castles with two turrets in between. There was a fort about every five Roman miles. It is thought that the mile-castles were staffed with static garrisons, whereas the forts had fighting garrisons of infantry and cavalry. In addition to the wall's defensive military role, its gates may have been used as customs posts.

Castle Black is the primary headquarters and redoubt of the Night's Watch. It is located roughly halfway along the length of the Wall on its southern side, at the northern end of the Kingsroad. It is a dark and chilling home to its garrison. It is one of only three manned castles left on the Wall along with Eastwatch-by-the-Sea and The Shadow Tower. There are nineteen castles along the Wall, but as their numbers fell over the centuries the Night's Watch had to abandon sixteen of them. Castle Black is located between the unmanned castles of Queensgate and Oakenshield.

These two vastly different, and yet fundamentally the same, fortifications serve the same purpose in their worlds, real or fictional. These two Walls were constructed out of the need to protect the citizens on one side of the Wall, and keep out those on the other side. Both structures have been left to ruin, lesser so in the case of Castle Black, and yet they are still extremely significant to the world they are in.