Background walls

Background walls, also just known as walls, are tiles that create backgrounds on top of biome backgrounds. Walls are hidden behind everything else, such as blocks. Natural walls are generated at world creation, being abundant in certain biomes like the Underground Jungle, and are of the main components a Terraria world consists of alongside blocks and liquids. Walls can be removed with a hammer or . Flammable walls can also be destroyed by fire or lava. There are currently 250 obtainable walls.
Many wall types exist as items that the player can place in their inventory and then re-place in any area which does not already have walls. Certain mechanics of walls is dependent on which of the following categories they fall under:
* Safe walls prevent enemies from spawning (but do not do anything to prevent their passage), and a mostly unbroken background of safe walls is necessary for a structure to qualify as a NPC house, or to use a Bed to change a player's spawn point. Safe walls are usually obtained from crafting, or purchased from NPCs, but can also be found naturally in certain structures, such as Shrines and Pyramids. 
* Unsafe walls are a type of wall that appears during world generation, and can generally not be utilized by the player; when broken, they will either drop their safe equivalent or nothing at all. Unsafe walls will not stop enemies from spawning, and cannot be utilized for houses. They also have a quirk in that they must be removed by starting from their edge (i.e., adjacent space with no wall), which for explosives means that an edge must exist somewhere within the radius of the explosion.
Distinguishing safe walls from unsafe walls can be tricky because many walls, such as Obsidian Brick Walls or Dungeon Brick Walls, exist in both safe and unsafe forms. With these walls (both of which are harvestable), the player must break the unsafe walls and replace them in order for them to count as safe walls. Similarly, many (or all, on ) naturally-generated walls have safe counterparts which are obtainable through crafting or purchase from NPCs. 
== Types ==
=== Crafted walls ===
These walls are made by the player using various crafting materials. All crafted walls qualify for housing.
=== Purchased walls ===
These walls are purchased from various NPCs. All purchased walls qualify for housing.
=== Harvested walls ===
These walls can be harvested in various places when exploring the world. Most of them can also be obtained through crafting. All harvested walls qualify for housing.
=== Converted walls ===
These walls are normally created by biome spread. They can also be made using Solution sprayed with the Clentaminator or the Terraformer, and on the they can also be crafted or purchased (with the exception of the natural Mushroom Wall). On the the Clentaminator is the only way the player can make these walls. These walls qualify for housing when they are crafted or purchased, but not if they are created by biome spread or the Clentaminator.
== Notes ==
* Dirt Walls generally completely cover the background at Underground depths above zero (see Layer, Depth Meter). Placing new walls in this area would require first tearing down the existing walls starting from the top (the Surface) or the bottom (zero depth), which can be an arduous task. Alternatively, the existing walls can be destroyed using explosives.
* At depths below zero, the backdrop of the map is generally no longer covered with actual wall tiles, though this can be difficult to differentiate visually since the biome background at these depths can have a similar appearance. Walls can be placed freely here by players.
* Torches and several other furniture items can be placed directly on background walls without requiring blocks below them.
* Most walls have no coin value, even if they were crafted from rare materials. Stained glass and wallpaper bought from the Painter are exceptions.
* Walls appear to have their own placement layer.
== See also ==
* Wall IDs
* Blocks
== History ==
== Footnotes ==