The Nobility designates all the Families whose members exercise or are able to exercise certain functions of military command and civilian command. These functions are a privilege granted to them by the King or similar authority.
Nobility is above all a social institution that we encounter in most of traditional societies, as soon as the warrior function is organized independently from the economical and religious Powers, as we can see in Celtic or early Roman societies.
Recruit of such Noble members was mainly made, as in other professions, through inheritance of Title in most Noble Family lineages. Or it could be made via the notion of Merit, thanks to challenges, competitions or contests.
At the basis, Nobility designated those who had enough power and wealth to proper arm, feed, and equip their defender Knights. After the Clergy (in this Guild represented by the Equilibrium), Nobility represented the second major Order, both having the same weight. The last Order concerned the rest of the mass, vulgarly called ‘Third State’. Members of Nobility had the obligation to occupy onerous byt costly functions, such as The Army, High Administration, Liberal Arts, etc… They were forbidden the access to lucrative functions such as Commerce, Craft, Banking,etc…
Blue, as the color of Royalty, quickly became the color of Nobility. Thus, ‘to have blue blood’ in an expression meaning: ‘to be from noble origin.’
Nobility can be summarized this way in the end: They are chosen people who are granted privileges from the King. They are landowners, have titles and wealth. In the end, most of the nobility became Knights, as a title, because it would fit their image. But they would take care of other Knights, the fighter ones, the real ones, because those Nobles needed protection.