Wall
From WikiManual
Walls are impenetrable barriers that allow creation of isolated or semi-isolated areas within a single simulation. Presently they are about the buggiest part of the program, so don't be surprised when you see your walls floating off into space or bots trying to eat your walls.
Currently these will cause a program crash, so are not recommended for use.--Endychat 17:12, 24 Nov 2005 (MST)