|This article is about an older version of DF.|
A sky support is an unusual quirk of dwarven physics whereby a natural or constructed tile attached to the sky (i.e., built on the top level of the map) will provide a limited form of support to the tiles directly below it. Any attempt to build off this column horizontally will result in a cave-in.
Sky support will override the "standard" support given to any tile connected to the ground. This behavior can cause previously supported constructions to collapse if their support columns become attached to the top level of the map. A clever application of this behavior allows the player to create some otherwise impossible cave-ins. For example, the player can collapse hundreds of z-levels of rock into the magma sea without channeling out the surrounding rock, and the player can even cause semi-molten rock to collapse. See this forum thread for full instructions.
This mechanic can be used to create a free-floating Skyfort.