Mortek Crawlers are constructs of the Ossiarch Bonereapers that act as arcane catapults that delivers death from afar. Designed by Katakros himself, it is as much a creature as it is a machine and the original diagrams are still pridefully displayed on the scroll-covered walls of the Mortarch's Chamber of Contemplation. 
The Mortek Crawler is a self-powered artillery device containing an aggressive animus and borne to war upon dozens of skeletal legs like a centipede and is able to fire on the move without a loss of accuracy. The winch-like apparatus at the crawler's side is powered by a turnwheel of bone, run by an Ossirach of the Mornial caste who while lacking the warrior skill has enough to work for eternity without pause. The war viziers on its vertical stanchions act as spotters and are well versed in identifying weak spots of armies and their command structures and they decide the type of esoteric ammunition the crew at the machine's rear will load into the claw and give the command for the torsion to be released. The reloading reloading and releasing of its arcane payload can be done in a matter of mere seconds. 
The Mortek Crawler has three principal types of ammunition, 
- Cauldron of Torment: Hollow artefact containing spirits too tortured by war and death to lend animus to a Bonereaper construct. These souls driven to insanity scream with soul-chilling anguish as the cauldron slams into the greater mass of the enemy, driving the survivors mad with fear. 
- Cursed Stele: Artefact inscribed with a death hex that grows more potent when the Mortek Crawler is attacked. When released the graven block land with bone-crushing force and then discharges its lethal curse on impact, causing anything struck by the stele to erupt in baleful flames, reducing them to charred bone-dust in moments.
- Necrotic Skulls: The skulls are left to absorb the unholy energies of the Shyish Nadir in the laboratories of Nagashizzar, filling them with morbid magic and giving the skulls an aura of blackest aether-smoke. Those struck by such missiles are subject to the full measure of those lethal energies, collapsing to the ground with a rictus of fear and agony twisting their features as their vital force suffers immeasurable damage.