Medieval theorists of nobility relied on earlier classical concepts (Platonic, Aristotelian and Christian-Hellenistic) of what personal traits and virtues constitute grounds for ennoblement.
Bartolus defined natural nobility by reference to Aristotle, who in his Politics explains how some are marked out for freedom by their virtues (and specifically by their capacity to rule), and are so distinguished from the mass of men whose talents fit them only for a servile role.
Bartolus argues that the prince should strive to make his dominion a true mirror of God's own by advancing only those who are naturally noble (see Maurice Keen, Chivalry, p. 149).
The counter-revolutionary author Edmund Burke wrote on merit-based promotion: "...the road to eminence and power, from obscure condition, ought not to be made too easy, nor a thing too much of course.
Napoleon Bonaparte and Friedrich Nietzsche were later to continue the tradition of promoting a vision of aristocratic meritocracy, although no longer within (and opposed to) the Catholic-chivalric framework.
After the reforms of Tsar Peter the Great in the early 18th century, noblemen in Russia were obliged to serve as civil or military officials.
The system was later extended to merchants and industrialists that with a successful career managing a business of reasonably large size would achieve personal or hereditary nobility.