Nurgle Plague Tower
The Plague Tower of Nurgle is a Daemon Engine from the Days of Epic... bet that already started the bells ringing, huh? It is a serious contender for the title of "Absolute Stupidest Chaos War Machine Of All", and considering some of the other Daemon Engines, that's saying something.
As the title suggests, it is, at heart, a glorified siege tower. Yes, the big towers on wheels that besieging forces would push forward to try and act as a ramp into the castle in medieval times. The sort of thing that even Feral Orks consider kind of primitive. Like its fellow Nurglite Engine, the Contagion, the Plague Tower is mostly made of rotting wood and rusting metal, held together more by Nurglite magic than anything. Unlike a primitive siege tower, though, it mounts two demolisher cannons, a "Pus Cannon" that spews diseased, corrosive slime at anything close by, and a disease-vomiting Plague Mortar on its top. The whole ramshackle contraption is also infested with Nurglings, which rally to defend it against invaders.
http://warhammer40k.wikia.com/wiki/Plague_Tower