From A Wiki of Ice and Fire
The Wall is a massive wall over 700 feet high and is made of ice, stretching 300 miles across the northern border of the Seven Kingdoms, separating it from the wild lands beyond. Appearing as one of the nine Wonders Made by Man in the book by Lomas Longstrider, the Wall is defended and held by the Sworn Brothers of the Night's Watch, who patrol and guard the castles from the Frostfangs mountain range in the west to the Bay of Seals in the east.
The Wall was reputedly created over 8,000 years prior to the present setting by Brandon the Builder after the Long Night to defend the realms of man from the wildlings and Others. Approximately 300 miles in length and 700 feet in height, the Wall is protected by the Night's Watch and according to some, ancient spells and sorcery. Supposedly, Brandon the Builder had placed his foundations along the heights wherever possible. Several mentions in the text suggest that the Wall was much smaller at the time, having been built upon by the Night's Watch builders, who quarried huge blocks of ice from frozen lakes in the haunted forest and dragged them south to make the Wall higher, raising it over the centuries to its present size. However, the severely reduced Night's Watch at the present time is limited to maintenance duty. A total of nineteen fortresses have been built along the Wall though only three, The Shadow Tower, Castle Black and Eastwatch-by-the-Sea are occupied at the start of A Song of Ice and Fire.
The Wall stretches for 300 miles and is approximately 700 feet tall, It is made of solid ice and stone, and can be seen for miles round. It appears grey or blue depending on the weather and time of day. The top is wide enough for a dozen mounted knights to ride abreast and it is thicker at the base. According to myth, there are old spells woven into it, to strengthen it and keep creatures of a magical nature such as the Others from passing it. 
The Wall is straight from Castle Black to Eastwatch-by-the-Sea, but runs like a snake between Castle Black and the Shadow Tower.
The Wall has no gates anywhere, simply a few tunnels cut through it that are secured by heavy iron bars and massive chains that must be unlocked. They are sealed with ice and stone wherever castles have been abandoned or in times of danger. 
The castles on the Wall, listed from west to east, are:
- Westwatch-by-the-Bridge, re-garrisoned
- The Shadow Tower, garrisoned, commanded by Ser Denys Mallister
- Sentinel Stand, re-garrisoned
- Greyguard, re-garrisoned, under the command of an unnamed steward from the Shadow Tower
- Stonedoor, re-garrisoned, under the command of Soren Shieldbreaker. Borroq is scheduled to join them
- Hoarfrost Hill, Jon Snow intends to re-garrison the castle but does not name a commander
- Icemark, re-garrisoned, under the command of Bedwyck
- The Nightfort, given over to Stannis Baratheon by Jon Snow
- Deep Lake, re-garrisoned, possibly with wildlings under the command of Halleck
- Queensgate, re-garrisoned by wildlings under the command of Morna White Mask
- Castle Black, garrisoned, commanded by Lord Commander Jon Snow
- Oakenshield, given over to Tormund as his seat
- Woodswatch-by-the-Pool, abandoned
- Sable Hall, re-garrisoned, possibly with wildlings under the command of Halleck
- Rimegate, Jon Snow intends the re-garrison the castle but does not name a commander
- Long Barrow, re-garrisoned by spearwives under the command of Iron Emmett
- The Torches, re-garrisoned
- Greenguard, re-garrisoned by wildlings under the command of Devyn Sealskinner
- Eastwatch-by-the-Sea, garrisoned, commanded by Cotter Pyke until his sailing to Hardhome. Ser Glendon Hewett commands in his stead
The Night's Watch permits the forest to come no closer than half a mile to the Wall. However, over time the places where abandoned Castles stand, the forest has crept back closer. The top of the wall is studded with catapults and cranes. During the Battle of Castle Black, Jon Snow wishes the catapults were on turntables after the wildlings learn the shun the area where the catapult's payload landed. Additionally, many catapults and trebuchets have been dismantled for repair and never reassembled after they're frozen in ice. The galleys of Eastwatch patrol the Bay of Seals in part to catch smugglers who bypass the wall through the sea and trade weapons to the wildlings and to the west the mountains and deep river Gorge, make the terrain impassable for all but small groups of raiders.
The Night's Watch raised nineteen castles to guard the hundred leagues of the Wall, however they had never manned more than seventeen at one time. Over the last three hundred years, as the manpower of the Watch has dropped, most of these castles have been abandoned; "the ghost castles" as some have come to call them.
Before the current phase of the Conflict Beyond the Wall, only three castles remain in use, though sometimes a larger force will be sent to one of the abandoned castles for a fortnight or a moon's turn as well, which was suggested by the First Ranger, Benjen Stark. The manned castles are:
- Castle Black, the largest maintained castle, located at the northern end of the kingsroad and held by nearly six hundred Brothers.
- the Shadow Tower, the westernmost of the occupied castles, garrisoned by two hundred men of the Night's Watch.
- Eastwatch, port of the Night's Watch with the smallest garrison of the Night's Watch.
The Wall provides a tremendous tactical advantage to its defenders, enabling a small group to hold off a much larger force. Defenders are generally beyond the range of bow shot or catapult and in turn rely on archery, catapult and dropped objects to deter an assault. In particular, barrels containing rocks frozen in ice are effective in dispersing a mass charge. 
Attackers must rely on one of two tactics, a direct assault on one of the few well-defended gates, or scaling the Wall in small groups and attacking a gate from the rear. The gates have been designed with features such as murder holes and limited access that make them difficult to force. In an extreme case, gates can be filled with rock and ice, thus becoming as impervious as any other part of the wall.
Scaling the Wall involves similar difficulties. A team of determined climbers can reach the top, but only if undetected by defenders, who can easily knock them off with dropped objects or archery. The Wall is thought to "defend itself", disgorging sheets of its own ice.
According to legend, the Wall is vulnerable to the Horn of Joramun.
A Game of Thrones
A Storm of Swords
A Dance with Dragons
- Greyguard, re-garrisoned by thirty men of the Night's Watch under the command of a Steward from the Shadow Tower.
- Stonedoor, given to the free folk led by Soren Shieldbreaker, to settle and garrison.
- Icemark, re-garrisoned with thirty men under the command of Bedwyck, twenty from the Night's Watch and ten of Stannis's men.
- The Nightfort, the largest castle on the wall. It was recently given to Stannis as his seat. It would take a long time to make it fit for habitation again.
- Deep Lake, re-garrisoned with free folk under the command of of a member of the Night's Watch.
- Queensgate, given to the free folk led by Morna White Mask to settle and garrison.
- Oakenshield, given to the free folk Tormund for his clan and seat of his power.
- Sable Hall, re-garrisoned with free folk under the command of of a member of the Night's Watch.
- Long Barrow, re-garrisoned with free folk spearwives, under the command of Iron Emmett.
- Greenguard, given to free folk of Devyn Sealskinner's clan to settle and garrison.
|“||Almost seven hundred feet high it stood, three times the height of the tallest tower in the stronghold it sheltered. His uncle said the top was wide enough for a dozen armored knights to ride abreast. The gaunt outlines of huge catapults and monstrous wooden cranes stood sentry up there, like the skeletons of great birds, and among them walked men in black as small as ants.||”|
- Jon Snow's first impression of the Wall
|“||If the Wall should ever fall, all the fires will go out.||”|
|“||You know nothing, Jon Snow. This wall is made o’ blood.||”|
|“||The Wall can stop an army, but not a man alone.||”|
Behind the scenes
References and Notes
- ↑ A Storm of Swords, Chapter 56, Bran.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 A Storm of Swords, Chapter 30, Jon.
- ↑ 3.0 3.1 3.2 A Game of Thrones, Chapter 19, Jon.
- ↑ SSM: The wall (September 09, 2000)
- ↑ A Game of Thrones, Chapter 48, Jon.
- ↑ 6.0 6.1 A Storm of Swords, Chapter 41, Jon.
- ↑ 7.0 7.1 A Game of Thrones, Chapter 21, Tyrion.
- ↑ A Storm of Swords, Chapter 54, Davos.
- ↑ SSM circumventing the Wall
- ↑ A Storm of Swords, Chapter 64, Jon.
- ↑ A Clash of Kings, Chapter 68, Jon.