- Samwell Tarly: "The White Walkers sleep beneath the ice for thousands of years. And when they wake up..."
- Pypar: "And when they wake up... what?"
- Samwell Tarly: "I hope the Wall is high enough."
- — The Pointy End
The Wall is a colossal fortification which stretches for 300 miles along the northern border of the Seven Kingdoms, defending the realm from the wildlings who live beyond. The Wall is reported to be over 700 feet tall and is made of solid ice. It was reportedly constructed using both magic and mundane means some eight millennia ago in the aftermath of the Long Night to defend the realm against the White Walkers who reportedly dwell in the uppermost north, although the White Walkers are now only considered to be mythical.
The Wall is defended and held by the Sworn Brothers of the Night's Watch. Once an honorable institution, by the time of the War of the Five Kings the Watch has fallen on hard times. It has become grievously under-strength, numbering less than a thousand men, an all-time low for the Night's Watch. While once great glory and honor was to be had in the Watch, in the present day it is often seen as a glorified penal colony.
The headquarters of the Watch is Castle Black, located in the shadow of the Wall at the northern end of the Kingsroad. Eastwatch, located at the eastern end of the Wall, serves as the main port and resupply post for the Night's Watch. The Shadow Tower at the western end of the Wall is the only other manned castle. Among the abandoned castles along the length of the Wall are the Nightfort and Deep Lake. The region south of the Wall is called the Gift and is also controlled by the Night's Watch.
In the past, the Night's Watch would send men out every morning to the north side of the Wall to cut down any trees growing within one mile of the structure, so the wildlings couldn't use any natural cover to approach the base of the Wall undetected. With the ranks of the Night's Watch drastically diminishing over the years, however, many of the areas between the three forts that are still manned have tall trees growing right up to the base of the Wall.
In the books
In the A Song of Ice and Fire novels, the Wall is about 700 feet tall and is defended by three manned castles, the Shadow Tower at the far western end, Eastwatch-by-the-Sea in the far east and Castle Black in the middle, where the Kingsroad meets the Wall. The top is wide enough for a dozen mounted knights to ride abreast and it is thicker at the base. Castle Black is the Watch's headquarters and primary redoubt. Sixteen additional castles stretch along the base of the Wall, but these are no longer permanently manned due to the Watch's lack of manpower. The Wall was allegedly built by Brandon the Builder after the War for the Dawn to defend against the return of the Others.
Numbered on the map at right, these are names of the other castles. Of these, only the Shadow Tower is still garrisoned at the start of the books (as well as Castle Black and Eastwatch, whose names are written out on this map).
- The Shadow Tower.
- Sentinel Stand.
- Hoarfrost Hill.
- The Nightfort.
- Deep Lake.
- Sable Hall.
- The Long Barrow.
- The Torches.
All nineteen castles were not built at the same time, and indeed many of them were constructed centuries apart. Castle Black actually isn't the original headquarters of the Night's Watch. The original headquarters was the Nightfort, the first castle built along the Wall, making it possibly eight thousand years old. The Nighfort is larger than all of the other eighteen castles that were subsequently built along the Wall. As the Night's Watch's numbers dwindled, the large castle was so understaffed that it became difficult to maintain. This ultimately led to the Nightfort being abandoned 200 years ago, and the headquarters of the Night's Watch was moved to Castle Black. It isn't clear exactly how old Castle Black is, but it wasn't purpose-built as a replacement for the Nightfort (the castle of Deep Lake was its replacement). Castle Black may have been built after the Andal Invasion, when there were fewer recruits who worshiped the Old Gods: note that Castle Black doesn't have its own godswood with a heart tree, thus Jon Snow has to swear his oath before a heart tree in the Haunted Forest on the other side of the Wall. Some of the other, older castles along the Wall (such as the Nightfort) do have godswoods.
Measurements in the Seven Kingdoms in both the books and TV series are given in imperial measurements. Converted to metric for the benefit of some viewers, the Wall is 482 kilometers (300 miles) long and between 213 and 244 meters (700-800 feet) tall.
In "Mhysa", Samwell Tarly says that the Wall is 500 miles long. This appears to be an error, as the books say clearly it is 300 miles long and the evidence in the TV show (such as the distances given for Winterfell to Torrhen's Square and the faster speed of travel between Winterfell and King's Landing) suggests that Westeros may actually be smaller than in the books, whilst the Wall being 500 miles long would actually may it substantially larger.