A 3D middle texture, often abridged as 3dMidTex, is a sort of simplified 3D floor without a floor or ceiling. Instead, a sector's midtextures are used to represent a solid barrier under and over which it is possible to pass. Without support for the Hexen map format and its Z-height field for things, the Eternity Engine developed first the capacity to flag a linedef as being a solid middle texture. In this way, there is no need to place an invisible brige thing; however the mapper needs to make sure the lattice of middle textures is dense enough to let actors walk on it without falling.