The subject of the Roman Jurisprudence was ever kept alive and active by the fact that the Christian Church had in a measure adopted it as her own. For it was from the Roman Civil Law that the Canon Law of Christian Rome was evolved. In the age of comparative freedom for the Church which followed from the accession of Constantine the Great to the Downfall of the Empire of the west, this evolution had gone on, and had increased in volume according as the power and influence of the Church had increased. In a certain sense the scope of this power and influence became greatly enlarged and vastly enhanced after the overthrow of the Empire, by reason of the fact that the Church was then called upon to protect the people against oppression and wrong by the barbarian conquerors, and by reason of the further fact that very soon afterwards the bishops of the Church were compelled by the force of circumstances to assume a large amount of temporal power and even to become princes and potentates equal, and often superior, to the greatest feudal nobles.
Many subjects were drawn within the cognizance of ecclesiastical law, some exclusively so, which previously had been more or less controlled by the civil authorities; and locally the bishops had their own courts wholly independent of the feudal tribunals. Even when the bishops held both classes of tribunals, as they often did, they were always careful to maintain the ecclesiastical jurisdiction separate from the ordinary civil power. Thus it was that the subject of marriage, the civil conduct of the ministers of the Church, the disposition of property granted to the Church for its uses, and various other analogous matters, were withdrawn from the feudal authority and subjected exclusively to the ecclesiastical jurisdiction. Then the monasteries and convents, which became numerous and were veritable republics, in fact the first constitutional republics within the feudal territory, sharply antagonized the tenets of Feudalism. All this caused a remarkable development of the ecclesiastical law, and naturally enough on the lines of the Civil Jurisprudence of Rome. And thus was the Roman Canon Law developed by successive popes and bishops and councils of the Church, as the Roman Civil Law had been developed by the praetors and commentators.
So, too, when the Canon Law, like the Civil Law, had become voluminous and required to be systematized, the work of Gaius, Papinian and Tribonian was paralleled by the learned Gratian of Bologna for the Church in A.D. 1150. From a mass of detached regulations Gratian produced a single, consistent, and easily accessible commentary on the whole ecclesiastical law, to which the title of Corpus Juris Canonici (Body of the Canon Law) was afterwards given, as the title of Corpus Juris CiVilis (Body of the Civil Law) had previously been bestowed on the great work undertaken by the order of Justinian. The City of Bologna, where Gratian taught, remained for many ages the great school of both; and it has been noted that it was its famous university which first conferred the degree of Doctor of Laws (LL.D.) meaning Doctor both of the Roman Civil, and of the Roman Canon Law.
It was rather indirectly through the Canon Law than directly of its own force that the Roman Jurisprudence first succeeded in checking the progress of Feudalism and subsequently in subverting the system. The Canon Law was the immediate weapon of the Church where with to antagonize the barbarian usages of Feudalism.