• To keep things in.
• To keep things out.
• To do both of the above.

History

As comedian Eddie Izzard once said, archaeologists always find a "...series of small walls". Walls have been around as long as there has been society. Society wanted to keep other tribes out, to keep their animals in, and to have shelter from the elements. These early walls may not be found during archaeological digs (having often been made of wood, animal dung and other degradable substances), but some of the techniques can be traced all the way through to walls that are still standing. A very good Entry on the ways that humans have built walls and structures out of their natural surroundings can be found at Earthbuilding - Building Using Natural Materials.

Often you may not be able to see the walls themselves, but you can see the earthworks that were built, to then be enhanced with fences and walls. Blewburton Hill, overlooking the village of Blewbury in the Vale of the White Horse, Oxfordshire, looks like it has rings around it. These earthworks, providing a series of ditches, were able to make walls effectively taller to provide better defence against invaders. All of the original walls have long gone, but the earthworks still remain.

Physical Walls

There are as many types of wall as there are materials to build with.

• 
  Walls that make up your house are likely to be made of bricks. These are cuboid shapes, made of fired clay and tend to be 22cm by 7.5cm by 7.5cm. They are not stacked on top of one another directly, but always offset by half of their length in order to make the wall more stable*. They are 'glued' together using mortar (made of sand, cement or lime, and water).
  
• Drystone Walls are used when mortar is easily washed away by poor weather, or when there was no access to mortar. They allow wind to filter through the wall, making it more likely to stay standing when battered by the elements. It is also easier to fix, quicker to build and longer lasting than a mortar-constructed wall.
  
• 
  Wooden walls, such as those found in chalets, are stacked logs. TO BE COMPLETED/MORE RESEARCH/HELP
  
• 
  Paper walls are a part of traditional Japanese buildings. Here thick rice paper is stretched over a wooden frame to provide privacy.
  
• 
  Walls made of metal are usually defensive in nature due to the extremely tough nature of the material. A vault, bars of a cage, or a room containing dangerous equipment are good examples.
  
• 
  A fire wall. Two types here:
  
  A computer program designed to block unwanted intrusions into your computer via the internet or other network.
  
  A literal wall of fire. This is most often found in fantasy universes, especially those involving magic, but also deserves a mention. Expansion needed.

Non-physical Walls

An immaterial or intangible barrier, obstruction, etc., suggesting a wall: a wall of prejudice.


Again, these can come into many forms. Immaterial walls tend to lean towards the conceptual. All of this probably needs refining.

• 
  Mental Block (such as Writer's Block). When there feels like a barrier between you and what you are trying to write, describe or verbalise.
  
• 
  Glass Ceiling. A perceived inability for a particular group in society to rise to higher levels, due soley to their belonging to such a group. This term is usually used to describe women who cannot be promoted due to discrimination against their sex, despite this being illegal in the countries where this phrase is commonly used.
  
• 
  Mental Walls. There is no set term for the mental barriers people place between themselves and the world, especially people. Some people place walls between people they don't know, and some people shut out others entirely. This may be due to a conscious decision, or due to episodes in their past tarnishing relationships with people. Really, really need some help here.
• 
  A wall of noise. Usually noise so loud and unpleasant it feels like a solid, tangiable wall.
  
• 
  'The wall' limit of physical fitness.
  
• 
  'Writing on the wall', 'First against the wall'- other phrases? Why are they important?
  

Famous Walls

There are all sorts of walls that deserve mention.


Great Wall of China is the longest wall ever built, and can be viewed from outer space. It was built to stop Mongols from invading the South part of the Chinese Empire.


Jericho is possibly the first recorded walled city ever. The first mention made of it is found in Numbers 22:1 of the Bible:

"Then the Israelites travelled to the plains of Moab and camped along the Jordan across from Jericho."


The only evidence that it had a wall, which seemed to be sort of metaphoric, states:>

"By faith the walls of Jericho fell, after the people had marched around them for seven days." -Hebrews, 11:30
Perhaps this was not a literal wall? Perhaps it is a mis-translation of the word 'wall'? Perhaps it meant a barrier of some other kind. More research needed.


The Berlin Wall. Link to this old BBC article perhaps?

Pop Culture

Not yet looked at. Really needs more to merit an entire section to it.

1. The Pink Floyd album The Wall was about a man who had an inability to socialise with others without panicking. This disability was in the metaphorical form of a Wall between him and everyone else. There was later a film made using the music of the album. The film contained no dialogue and instead used the images of the music, along with artwork by Gerald Scarfe to convey the storyline.