Seeking a less vacuous species of explanation, we are soon led to recognise (1) that the case of medieval Italy was to the extent of at least two factors more complicated than that of ancient Greece; and that these factors alone might suffice to explain their non-production of a "theory" which should avail for the need; (2) that the theories of the Greeks did not avail to solve their problem; and (3) that the Italians all the while had really two theories too many. At the very emergence of their republics they were already possessed or wrought upon by the embodied theories of the Empire and the Papacy, two elements never represented in the Greek problem, where empire was an alien and barbarian thing suddenly entering into the affairs of civilised Hellas, and where there was nothing in the nature of the Papacy. These two forces in Italian life were all along represented by specific theories; and their clash was a large part of the trouble. Their pressure set up a chronic clash of parties; and the theorist of to-day may be challenged to frame a theory which could have worked well for Italy otherwise than by setting those forces aside--a thing quite impossible in the Middle Ages. If mere system-making on either side could have availed, Thomas Aquinas might have rendered the service.[603] The economic and political destiny of the Church may be said to have been determined in the eleventh century, when, after a desperate struggle, begun by Pope Hildebrandt, celibacy was forced on the secular clergy. The real motive to this policy was of course not ascetic but economic, the object being to prevent at once the appropriation of church property by married priests for family purposes, and the creation of hereditary titles to church benefices. An evolution of that kind had actually begun; and there can be no question that had it not been checked it would have been fatal to the Papacy. Naturally the married clergy on their part resisted to the uttermost. Only the desperate policy of Hildebrandt, withdrawing popular obedience and ecclesiastical protection from those who would not give up their wives, broke down the resistance; and even thereafter Urban II, as we saw, had to resort to the odious measure of making priests' wives slaves.[604] From that period we may date the creation of the Church as a unitary political power. Sacerdotal celibacy took many generations to establish; but when once the point was carried it involved a force of incorporation which only the strongest political forces--as at the Reformation--could outdo, and which since the Reformation has kept the Church intact.