The term is here used in its narrower sense to stand for the Christian polity, an ideal which lasted for many centuries. Its foundations are to be found in Jewish traditions of a theocracy. From the Peace of the Church proclaimed by Constantine to the inroads of the barbarians, Christendom was all but conterminous with the Roman Empire, but imperial traditions were so strong that the ideal was not perfectly realized. At first the Christian polity seemed to perish with the empire. The subsequent ideal of the Middle Ages was influenced by De Civitate Dei (The City of God) of Saint Augustine. Charlemagne again made Christendom a temporal polity in the West. The revived empire in the 10th century was an imperfect copy of the Carlovingian. Otto III tried to make the empire more spiritual. In the 12th century the ecclesiastical body became a real society, cosmopolitan through the universal language, Latin; and the papacy was the head in temporal as well as spiritual things. An important part was played by the religious orders in unifying thought. The Franco-Norman civilization which developed in France, England, and southern Italy, created Gothic architecture and epic and lyric poetry. Clergy and laity have probably never since been so united. Pope Innocent III failed to realize his ideal of Christian cosmopolitanism, and after him the power of the papacy declined. The 14th century was a time of national wars, the Great Schism, and the unimpeded progress of the Turk. The development of nationality and of secular law proved factors in the Reformation. The Church lost influence over thought, and heresy affected faith and morals. Since the confusion caused by the Reformation the word Christian has come to express our common civilization, rather than a religion which so many Europeans no longer profess.