According to the ''Liber Armorum'', work on the Achilles was begun as a joint venture between Imperial Fist [[Techmarines]] and the [[Magos|Archmagos]] of [[Xan-Ebon]] in response to a pocket xeno-empire {{Fn|1}} that used fearsomely potent energy weapon{{Fn|4}} and was located far to the galactic south. Though their name has since been forgotten to the sands of time, the xenos had nevertheless managed the impressive feat of bogging down an entire [[Crusade]], necessitating the design of the Achilles. However the ancient mysteries used in the Achilles' final construction prevented any sort of mass production, such that by the [[Horus Heresy]] its use had not extended beyond the spearhead units of the Imperial Fists themselves, along with certain gifts delivered to the [[Dark Angels]], [[Thousand Sons]] and [[Salamanders]]. By the time of the [[41st Millenium]] the Land Raider Achilles exists in small numbers throughout a number of Space Marine [[Chapters]], though fittingly only the Imperial Fists and their successors field them in significant quantities, while outside the [[Adeptus Astartes]] it is said only the [[Ordo Reductor]] of the [[Adeptus Mechanicus]] maintains access to the design. The inability to mass produce the tank means each individual machine has its own idiosyncrasies, while even the rumour of a nearby wrecked or abandoned Achillies is enough to divert an entire Space Marine strike force to reclaim it.{{Fn|1}}

The most secret arts of the Cult Mechanicus went into the construction of the Achilles' structure, such that only a supreme [[Master of the Forge]] or [[Enginseer]] Artificier could comprehend and produce them. Ancient electromagnetic incantations and ferromantic computational algorithms were etched at a molecular level at each and every layer of its fabrication. {{Fn|1}} Every cantimeter of the surface of Achilles is etched with the most secret runes of the techno-magi, and the sigils inlay with meta-conducting zirconium.{{Fn|4}} The resulting tank is almost impossible to harm with any sort of projected energy weapon and only a massive kinetic impact is guaranteed to destroy it.{{Fn|1}}

 *{{Endn|4}}: [[Imperial Armour Volume Two (Second Edition)]], pg. 38