Solar Auxilia - A Tradition of Service: By the second standard century of the Great Crusade, Solar Auxilia Pattern forces formed perhaps 20%-25% of the overall Human strength of the Imperialis Auxilia's void-faring first-line armies, with numbers ranging into the tens of millions.By the time of the Horus Heresy, in terms of deployment, this force was split, with about two-thirds of the Solar Auxilia cohorts stationed permanently within the Imperium's boundaries divided into taskforce and garrison commands, and the other third separated out into various expeditionary fleets, Rogue Trader detachments and deep-range pathfinder ships on the ever-expanding and increasingly remote Imperial frontier.As they were particularly suited and organised so that they had few ties to home and could easily operate as detached commands, it became common for many smaller-scale expeditionary fleets which did not feature any substantial Legiones Astartes presence to be led by a core of Solar Auxilia under the particular authority of a general officer with the rank of "Lord Marshal" appointed by the Imperial War Council. The temporal power and authority of these lords marshal (and the most senior among them, the "Lords Militant Imperialis") were formidable in their own right.  It was from them and the ranks of their subordinate staff and warship captains that future colony Imperial Commanders were often drawn, and new Rogue Traders granted their Warrants of Trade.With the potential prize of absolute power under the Aquila over whole worlds as a draw, it is then unsurprising that commissions of rank within Solar Auxilia cohorts destined for the frontier became a thing sought after by ambitious officers, petty nobles and the scions of great houses of Terra alike. Some such commissions were earned and others acquired by more direct means, but fate and the limitless dangers of battle and alien worlds unnumbered served in most cases to weed out those whose ambition outweighed their aptitude swiftly enough.Regardless of this, it is the salutary truth that the pursuit of plunder as well as the quest for personal wealth and power were motivations that often served the Great Crusade just as well as duty and the desire for glory and belief in the unification of Humanity.For those of the lower ranks, the lure of service ultimately may have been more prosaic, but no less valuable; fine living standards, pay and the respect of the Imperium for their life's blood. And if they desired it, upon retirement after serving a minimum tour of thirty standard years' service, they received full citizenship and commensurate land, money and position in a newly settled or newly-Compliant colony world.For the many that chose to serve several tours and for whom the Solar Auxilia became a consuming way of life, the eventual reward was greater, and they were furnished with basic anti-agathic and medicae treatments to extend their lifespans and military usefulness accordingly.At its core, the Solar Auxilia became and remained a hardened body of professional soldiery, equipped and trained to the highest standards of the Imperium's mortal Human forces, and a keystone of the Great Crusade's tremendous progress.