The origins of the organization are traced to pre-Imperial times as they stood as part of the armed forces of the Mechanicum of Mars. According to legend, they were reported to have entered into the Calixis Sector during the Angevin Crusade for reasons of their own. Their duty was the protection of the Cult Mechanicus strongholds within that region of space. Their base of operations within that area is within the Lathes system, which serves as a mustering ground for the Myrmidons, who often are dispatched in small bands to reinforce the defences of the Mechanicus as well as to seek out and destroy their enemies. Whilst they are largely independent, they are linked to the Archmagi of The Lathes who serve as guarantors of their dominion.
The Myrmidons are noted as being expert killers as well as weapon masters and destroyers. They are often sent at the behest of the Archmagi of Forge Worlds to accompany Explorator during their expeditions of dangerous sectors of space as well as aid in the capture of the most dangerous of Xenos specimens. Some of the members of the Auxilia Myrmidon are also sent on missions involving renegade Techpriests who are accused of the foulest of techno-heresies and are thus targeted with extreme prejudice. To aid them in their tasks, some of these Myrmidons are known to carry ancient and powerful weapons that are relics of the distant past.
Members of the Auxilia Myrmidon are noted as being towering figures who possess numerous hard points for weapons of arcane design. They are great war makers with knowledge of siege craft, devastation and weaponry, such that few can match their abilities. Whilst they are few in number, they are heavily augmented with the most powerful of their ranks being nearly impossible to kill. They are a source of fear and awe amongst the worshipers of the Machine God and are cybernetically reconstructed to a level beyond that of Enginseers and precepts.