The canon law, codified by Gregory IX. (1227-1241), was planned to rival the Corpus Juris Civilis. The Popes, with varying degrees of success, tried to render such international justice as the discordant elements introduced by the growth of cities and rise of nationalities demanded.[24] From the Council of Constance (1414-1418), which was a recognition of the fact of nationality, and at which the emperor for the last time appeared as the great international head, the decline of both the Church and the Empire as direct international factors was rapid.
(_c_) =Feudalism.= By the eleventh century feudalism had enmeshed both the temporal and spiritual authorities. This system, closely related to the possession of land and gradation of classes, discouraged the development of the ideas of equality of state powers necessary for the development of international law, though it did emphasize the doctrine of sovereignty as based on land in distinction from the personal sovereignty of earlier days.
(_d_) =The Crusades= (1096-1270), uniting Christendom against the Saracen for foreign intervention, awakening Europe to a new civilization, expanding the study and practice of the Roman law which feudal courts had checked, weakening many feudal overlords, enfranchising towns, freeing the third estate, spreading the use of the Latin language, enlarging and diversifying commerce, teaching the possible unity of national interests, led to the apprehension of a broader basis in comity which made the growth of interstate relations more rapid.[25]
(_e_) =Chivalry.= The code of chivalry and the respect for honor which it enjoined introduced a basis of equable dealing which on account of the international character of the orders of chivalry reacted upon state practice throughout Christian Europe.
(_f_) =Commerce and Sea Laws.= The expansion of commerce, especially maritime, emphasized the duties and rights of nations. The old Rhodian laws of commerce, which had in part been incorporated in and expanded by the Roman code during the days before the overthrow of the Empire, formed a basis for maritime intercourse. From the fall of the Empire to the Crusades commerce was attended with great dangers from pirates on the sea and from exactions in the port. The so-called _Amalfitan Tables_ seem to have been the sea law of the latter part of the eleventh century. The much more detailed _Consolato del Mare_ of doubtful origin between the twelfth and fourteenth centuries derived some of its principles from the eleventh-century code. The _Consolato_ was recognized by maritime powers as generally binding, and made possible wide commercial intercourse. Many of its principles have stood to the present day, though touching such questions as the mutual rights of neutrals and belligerents on the sea in time of war.[26] As the _Consolato_ formed the code of Southern Europe, the _Laws of Oleron_ formed the maritime code for Western Europe, and were compiled the latter part of the twelfth century, whether by Richard I. or by his mother Queen Eleanor is a disputed question. These laws are based in large measure on the other existing systems. The _Laws of Wisby_, dating from about 1288, supplemented the _Laws of Oleron_, and formed the fundamental law of maritime courts of the Baltic nations.[27] The Hanseatic League in 1591[28] compiled a system of marine law, _Jus Hanseaticum Maritimum_, based on the codes of Western and Northern Europe. The maritime law of Europe was practically unchanged for nearly a hundred years, when systematized in 1673 under Louis XIV. Similar to the maritime codes are the "Customs of Amsterdam," the "Laws of Antwerp," and the "Guidon de la Mar."[29]