The Thanatar-class Siege Automata is a heavy class of Imperial robot utilised by the Legio Cybernetica during the Great Crusade and Horus Heresy eras of the late-30th and early 31st Millennia. Designed as a mobile artillery platform rather than a general battle unit, it is armed with a Hellex Pattern Plasma Mortar. This is a terrifying weapon able to launch dense spheres of blazing plasma on arcing trajectories over defensive barriers and into the heart of enemy fortifications, incinerating anything in their blast radius with a liquid tide of sun-hot fire.
The Thanatar's frame, built to accommodate the huge weapon and the power systems and fuel reserves required to supply it, is considerably larger than even the hulking Castellax-class Battle-Automata. Its frame is also heavily reinforced, both to withstand the stresses of firing its principal weapon and to protect it from incoming attacks. This factor, alongside the use of an Atomantic Shield array, make Thanatars notoriously durable. Such is their resilience that Thanatars are beyond the ability of most small arms, no matter how advanced, to harm. It is not known if this particular class of heavy-siege automata is still utilised by the mysterious Legio Cybernetica in the late 41st Millennium.
Unlike many of the Battle-Automata produced to enhance the Mechanicum's military power during the Great Crusade, the origins and lineage of the Thanatar Pattern remain uncertain, save perhaps for the fact that its armament was known to be the product of the Forge World of Ryza. Ryza remained the only locale where the Hellax Pattern weaponry utilised by the Thanatar was produced during the time of the Great Crusade.
- Thanatar-Calix-class Siege Automata - The Thanatar-Calix-class Siege-Automata is a potent war machine and a wonder of the Mechanicum's craft. Combining arcane and secret technologies, it carries a twin-linked Mauler Bolt Cannon alongside a rare Solex Pattern Heavy Lascannon, whose beams of coherent light can reach far across a battlefield to lethal effect. The Thanatar-Calix's most destructive armament though is the Graviton Ram, a weapon whose origins are lost in the Dark Age of Technology. The ram's crushing waves of gravitational force can pulverise infantry and vehicles alike, and it can be utterly devastating at both range and close quarters. The Thanatar's frame, designed as a heavy weapons platform, is well-armoured and further protected by Atomantic Shield generators, making it nearly impervious to all but the heaviest of weapons fire. Whilst it is slow to advance, the Thanatar-Calix's durability allows it to close steadily on its target, moving ever-nearer until its formidable weaponry can be brought into range.
- Thanatar-Cynis-class Siege Automata - Unlike the lauded Thanatar-Calix, this variant of the potent Thanatar-class Siege Automata, known as the Cynis, was met from its creation by the Magi of Estaban III with ill-fortune and acrimony. An unashamed attempt by the Mechanicum faction on Estaban to increase their power within the order of the Machine God's domains, the Cynis was intended to replicate the Thanatar Siege-Automata on a wider scale. By doing so, the Magi of Estaban perhaps hoped to further usurp the sometimes troublesome Forge World of Ryza's importance in the eyes of the Fabricator-General. Without Ryza's mastery of plasma-arcana however, the Cynis proved an unstable and often self-destructive design, despite its obvious battlefield power; its Machine Spirits were equally believed to be erratic and malevolent by those Adepts whose task it was to tend them. Regardless, the Fabricator-General approved its design over the strong objectives of Ryza, worsening the feud which had broken out between Ryza and Estaban III, although the production of the class was far less successful than hoped. Accusations of sabotage and malifica by Estaban on the covert agents of Ryza were commonplace before the outbreak of the Horus Heresy, and when Estaban III declared for the Traitors and Ryza the Loyalists, bitter blood could at last be settled with iron and fire.
- 1 to 5 Thanatar-class Siege Automata (comprising a Maniple)
- Hellex Pattern Plasma Mortar - Shunning the crude shells favoured by most siege guns, the Hellex Plasma Mortar fired high-density charges of burning plasma in programmed trajectory arcs timed to detonate over their targets. These airbursts created rolling waves of incinerating energy which engulfed the surrounding area, burning through anything they encountered.
- Twin-linked Mauler Bolt Cannon - The Mechanicum utilised a variety of Bolter weaponry which, while operating on similar principles to the standardised weapons of the Legiones Astartes, were often more sophisticated and difficult to maintain. Such weapons include the Mauler Pattern Bolt Cannon, a fearsomely-baroque and bulky automatic cannon using substantially larger and denser shells than a standard Heavy Bolter.
- Infravisor - This simple visor allows its user to see across a wide range of the electromagnetic spectrum. So equipped, they can see better in low-light conditions than a normal human could see in optimal daylight.
- Atomantic Shielding - Certain Battle-automata featured particularly powerful Atomantic Reactor cores designed to energise defensive field generators built into the Battle-automata's exterior armour plating, as well as power its combat systems.
- Enhanced Targeting Array
- The Horus Heresy - Book Three: Extermination (Forge World Series) by Alan Bligh, pg. 227
- The Horus Heresy - Book Five: Tempest (Forge World Series) by Alan Bligh, pg. 226
- The Horus Heresy - Mechanicum Taghmata Army List (Forge World Series) by Alan Bligh, pg. 52
- Forge World - Thanatar Siege-Automata
- Forge World - Thanatar Siege-Automata Triptych
- Forge World - Thanatar Calix