|This article is about an older version of DF.
- A section of the cavern has collapsed!
A cave-in is what happens when there are no walls, supports, or other non-walkable tiles (including trees and rivers) in a revealed section of cavern 7x7 or larger. Mining out an overly large room will not result in an immediate cave-in - the room will appear to be stable, but after about a week and a half it will abruptly collapse. If a support holding up a 7x7 section is triggered by a lever or pressure plate, though, the cave-in is immediate.
If your fortress contains any rooms with unsupported ceilings, the message "You hear a deep rumbling coming from the cavern." has a chance to appear several days before the cave-in occurs.
A cave-in produces a dust cloud which knocks dwarves unconscious, as well as several tiles of unmined rock (with varying levels of damage, similar to that from mining) until there are no longer any 7x7 unsupported areas.
Any unit standing beneath a cave-in will be instantly killed, whether by the collapsing ceiling or by "falling rocks". Most items beneath a cave-in will also be destroyed, but light/dark stone, rough gems, ores, and corpses will instead be encased in stone and will become available once the debris is excavated.