Background walls

Background Walls are tiles that create backgrounds. Most wall types are items that can exist in player inventories, and can be placed by players in any area that doesn't already have background walls. Walls can be removed with a Hammer. All walls fall under two categories.
 * Housing walls are placed by players or generated in certain structures. They prevent enemies from spawning, but do not do anything to prevent their passage, and a mostly unbroken background of housing wall tiles is necessary for a structure to qualify as a House for attracting NPCs, or to place a Bed that can set a player's spawn point.
 * Natural walls are instead found throughout the world in several Biomes, and cannot be placed by players. Most natural walls were able to be crafted and placed by players if there is a workbench placed in a Graveyard, and if the player has the right materials for it. Natural walls will not stop enemies from spawning, and cannot be utilized for Houses, but natural walls made by players act like normal walls. These walls must be removed by starting from their edge (i.e., there must be at least one adjacent tile with no wall or housing wall), unlike housing walls, which can be removed from any point. Explosives can remove all natural walls within their blast radius as long as an edge is somewhere within the radius.

Certain walls, such as Obsidian Brick Walls or Dungeon Brick Walls exist in both natural and housing forms. With these walls, the player must break the natural walls and replace them in order to allow them to count as housing walls. Furthermore, the natural form of some walls, such as Dirt Walls or Jungle Walls cannot be harvested, and must instead be crafted or purchased from an NPC.

Walls are generally obtained via crafting, purchasing from NPCs, or by harvesting naturally-occurring walls. One item of crafting material generally crafts four of its corresponding Wall items. Most walls can also be crafted back into the items they were made from (four walls to one item), except for any wall crafted from more than one ingredient (e.g., Stained Glass).

Wooden Fence.png Crafted Walls
These walls are made by the player using various crafting materials.

Rainbow Wallpaper.png Purchased Walls
These walls are purchased from various NPCs.

[[File:Hive Wall.png]] Naturally Occurring Walls
These walls are spawned when the new world is created, and can all be obtained by some method.

Hallowed Grass Wall.png Converted Walls
These walls are mainly created when the Corruption, Crimson, or Hallow naturally spreads to them, but they can also be made by using the respective Solution with the Clentaminator. When destroyed, these walls do not drop anything. This technically makes them unobtainable.

Obsidian Back Wall.png Unobtainable Walls
These walls are spawned when the world is created but are unable to be created, obtained, looted, purchased, or used by the player in any way. They can be destroyed, but drop nothing (with an exception).

As of version 1.4, crafted versions of these walls can be created in Graveyard biome with Ecto Mist. (See "Crafted walls" above, where each numbered variant also gets its own name.) While they appear visually identical (or nearly so) to the natural walls, they may show a border when placed next to the natural version. The crafted versions also do not spawn enemies, and qualify for NPC Housing.

History
Hintergrundwände Murs de fond 벽면 Стены 背景墙