In the language of most superior jurisdictions in the end of the Middle Ages, the concept of enormitas included the most serious breaches of the legitimate order. It is suggested here that this concept was created during the 12th century in the practice of papal government and ecclesiastical reform. First, around 1130-1150, an « enormity » refered to a simple canonical irregularity without indicating any level of seriousness. From 1150-1160 on, the meaning changed. « Enormity » started to denote a blend of breach of rules or law, sin or stain and potentially radical subversion of the christian order. Although it remained typical of the ecclesiastical sphere, this new concept quickly spread broadly in the secular world, with a sense that was very similar to that of roman « atrocity » but had specific features. The enormitas of the 13th and 14th centuries was structurally unstable and protean. The perimeter of its field as a legal definition was variable, just as were its procedural implications. In many cases, the concept tended to embrace the whole criminal sphere (or « grand criminel », as it was called in France). Its use developed in concomitance with the rise of inquisitorial or « extraordinary » procedures, which were defined by an unprecedented expansion of the arbitrium judicis and therefore by situations of more or less generalized exceptionality with regard to traditional rules. While contributing to delimit the criminal sphere, enormitas thus created a continuum between the restricted field of crime of lese-majesty and that of ordinary crimes.