In the confusion arising from the long and varying contest as to the boundaries of civil and ecclesiastical jurisdiction, it is not easy to determine the exact influence which this decretal may have exercised directly in secular jurisprudence. We have seen above that the ancient form of absolute oath was still employed without change until long after this period, but the moral effect of so decided a declaration from the head of the Christian church could not but be great. Another influence, not less potent, was also at work. The revival of the study of the Roman jurisprudence, dating from about the middle of the twelfth century, soon began to exhibit the results which were to work so profound a change in the legal maxims and principles of half of Europe.[204] The criminal procedure of the Barbarians had rested to a great degree on the system of negative proofs. In the absence of positive evidence of guilt, and sometimes in despite of it, the accused was bound to clear himself by compurgation or by the ordeal. The cooler and less impassioned justice of the Roman law saw clearly the futility of such attempts, and its system was based on the indisputable maxim that it is morally impossible to prove a negative—unless, indeed, that negative should chance to be incompatible with some affirmative susceptible of evidence—and thus the onus of proof was thrown upon the accuser.[205] The civil lawyers were not long in recognizing the truth of this principle, and in proclaiming it far and wide. The Spanish code of Alfonso the Wise, in the middle of the thirteenth century, asserts it in almost the same words as the Roman jurisconsult.[206] Not long before, the Assises de Jerusalem had unequivocally declared that “nul ne peut faire preuve de non;” and Beaumanoir, in the _Coutumes du Beauvoisis_, approvingly quotes the assertion of the civil doctors to the same effect, “Li clerc si dient et il dient voir, que negative ne doit pas quevir en proeve.”