Dungeon Brick Walls

Dungeon Brick Walls are the background Walls found naturally-placed in Dungeons. There are a total of 9 different variants, but each Dungeon can include only the three wall types matching that Dungeon's bricks. A single Dungeon will usually contain all three types in different areas; in each area, the Faction Flags found will correspond to the wall variant.

Dungeon Brick Walls cannot be crafted (nor converted into Dungeon Bricks), but can be freed and collected with a Hammer or Dynamite after Skeletron has been defeated. As with other naturally-placed walls, natural Dungeon Brick Walls can only be mined from one of their edges (meaning that the wall tiles to be mined must be adjacent to empty tiles or player placed walls). As usual for natural walls, once they have been collected and placed by players, Dungeon Brick Walls will no longer count as natural; they will then prevent enemy spawns, and can be used for valid NPC Housing.

Variants
The type of Dungeon Brick Wall present in an area of the Dungeon, as well as the Faction Flags found there, will indicate which types of Hardmode Dungeon enemies are most likely to spawn there after defeating Plantera. Enemies matching the wall type have a ~90% chance to spawn, while other enemies have ~5% chance. Removing Faction Flags and/or placing them elsewhere will not affect enemy spawns; the natural flag placement is merely a hint, matching the background walls. As above, if any of the types is harvested and (re)placed by a player, it no longer counts as a natural wall, and will not spawn enemies at all.