From Blackstone:
But the common law of England, being not committed to writing; but only handed down by tradition, use, and experience, was not so heartily relished by the foreign clergy; who came over hither in shoals during the reign of the conqueror and his two sons, and were utter strangers to our constitution as well as our language. And an accident, which soon after happened, had nearly completed its ruin. A copy of Justinian's pandects, being newly discovered at Amalfi, soon brought the civil law into vogue all over the west of Europe, where before it was quite laid aside and in a manner forgotten; though some traces of its authority remained in Italy and the eastern provinces of the empire. This now became in a particular manner the favorite of the popish clergy, who borrowed the method and many of the maxims of their canon law from this original. The study of it was introduced into several universities abroad, particularly that of Bologna; where exercises were performed, lectures read, and degrees conferred in this faculty, as in other branches of science: and many nations on the continent, just then beginning to recover from the convulsions consequent upon the overthrow of the Roman empire, and settling by degrees into peaceable forms of government, adopted the civil law, (being the best written system then extant) as the basis of their several constitutions; blending and interweaving it among their own feudal customs, in some places with a more extensive, in others a more confined authority.
Nor was it long before the prevailing mode of the times reached England. For Theobald, a Norman abbot, being elected to the see of Canterbury, and extremely addicted to this new study, brought over with him in his retinue many learned proficients therein; and among the rest Roger surnamed Vacarius, whom he placed in the university of Oxford, to teach it to the people of this country. But it did not meet with the same easy reception in England, where a mild and rational system of laws had been established, as it did upon the continent; and, though the monkish clergy (devoted to the will of a foreign primate) received it with eagerness and zeal, yet the laity, who were more interested to preserve the old constitution, and had already severely felt the effect of many Norman innovations, continued wedded to the use of the common law. King Stephen immediately published a proclamation, forbidding the study of the laws, then newly imported from Italy; which was treated by the monks as a piece of impiety, and, though it might prevent the introduction of the civil law process into our courts of justice, yet did not hinder the clergy from reading and teaching it in their own schools and monasteries.