Lessons still to be learned by us from the study of both the success and the failure of Greco-Roman civilization; how the consideration of these may at once sober our expectations and inspire us with hope in the present. The forces which created it still maintain it and show no signs of exhaustion. But that they may continue in effect we must study these forces and learn the lessons the ancient experience of their working conveys, exerting ourselves first to understand Greco-Roman thought and practice and then to better their instruction. CHAPTER IV. THE MIDDLE AGES I. The mediaeval world. Geographical extent. Economic structure: its features of uniformity and isolation: the effect of the rise of a national economy on mediaeval society. Linguistic basis. Mediaeval scheme that of a general European system of estates rather than of a balance of powers. II. The unity of mediaeval civilization in its great period (1050-1300) ecclesiastical. The attempt of the Church to achieve a general synthesis of human life by the application of Christian principle. (1) The control of war and peace and the feudal world: the Truce of God and the Crusades: the papacy as an international authority: the mediaeval conception of war. (2) The control of trade and commerce and the economic world: just wages and prices: the mediaeval town. (3) The control of learning and education and the world of thought: reconciliation of Greek science and the Christian faith: allegorical interpretation of the world and its effects on natural science. III. The mediaeval theory of society. The organic conception of society: mediaeval thought _naturaliter Platonica_. The one society of mankind. Hence (1) little conception of the State or sovereignty or State law; but the universal society has nevertheless to be reconciled in some way with the existence of different kingdoms. Hence, again, (2) no distinction of Church and State as two separate societies: these are two separate authorities, _regnum_ and _sacerdotium_, but they govern the same society. The one society of mankind an ecclesiastical scheme uniting a great variety of personal groupings. IV. The influence of law on the development of the kingdom into the state--a process begun early in England and France, but only generally achieved about 1500. The new conditions--geographical, economic, linguistic--which prepare the way for the new world of the sixteenth century. The gulf between that world and the old mediaeval world. The hope of unity to-day. CHAPTER V. UNITY AND DIVERSITY IN LAW