In the same manner, as representing what was common to and valid throughout all Europe, nobility, and more particularly knighthood, centred in the Empire. The great Orders of Chivalry were international institutions, whose members, having consecrated themselves a military priesthood, had no longer any country of their own, and could therefore be subject to no one save the Emperor and the Pope. For knighthood was constructed on the analogy of priesthood, and knights were conceived of as being to the world in its secular aspect exactly what priests, and more especially the monastic orders, were to it in its religious aspect: to the one body was given the sword of the flesh, to the other the sword of the spirit; each was universal, each had its autocratic head[286]. Singularly, too, were these notions brought into harmony with the feudal polity. Cæsar was lord paramount of the world: its countries great fiefs whose kings were his tenants in chief, the suitors of his court, owing to him homage, fealty, and military service against the infidel. [Sidenote: Persons eligible as Emperors.] One illustration more of the way in which the empire was held to be something of and for all mankind, cannot be omitted. Although from the practical union of the imperial with the German throne none but Germans were chosen to fill it[287], it remained in point of law absolutely free from all restrictions of country or birth. In an age of the most intense aristocratic exclusiveness, the highest office in the world was the only secular one open to all Christians. The old writers, after debating at length the qualifications that are or may be desirable in an Emperor, and relating how in pagan times Gauls and Spaniards, Moors and Pannonians, were thought worthy of the purple, decide that two things, and no more, are required of the candidate for Empire: he must be free-born, and he must be orthodox[288]. [Sidenote: The Empire and the new learning.] [Sidenote: The doctrine of the Empire's rights and functions never carried out in fact.]