Over the course of the “long twelfth century,” the law of the western Church was transformed in ways which made it look very different from what it had been before. To denote the most fundamental aspect of that change, historians have used the word “systematization,” which accurately describes key developments in the intellectual life of the period. However, events that culminated in the appearance of the Concordia discordantium canonum (around 1140) and secured its author, Gratian, distinction as “the father of the systematic study of canon law,” can also be understood in terms of “reinvention,” which appropriately points to a qualitative break away from older legal practices. To speak of canon law as having been “reinvented” acknowledges that some form of it had been in place earlier on. “Systematization,” on the other hand, figures in the modern western mind as an expression that lacks distinctiveness in connection with legal matters. Audiences today are surrounded by a juristic culture that grew out of Gratian’s pioneering effort, and his approach to individual norms as elements of a logically coherent system is now considered to be the only plausible one.

A history of ecclesiastical criminal law has yet to be written. In this limited space, we will not attempt to accomplish such an ambitious task. Instead, the aim will be to provide a general overview of how medieval ecclesiastical law contributed to the development of public criminal law.

Apart from the very important profession of faith, the Council of Nicaea also promulgated twenty canons, most of which do not receive the same attention in research as the Nicene Creed, although these were already highly esteemed in ancient times. First of all, this chapter provides a brief review of their textual transmission. Besides the original Greek text, which has been handed down in canonical collections and writings of ecclesiastical writers, there are some translations into other ancient languages (Latin, Syriac, Coptic). Then after dividing the twenty canons into various thematic groups (for example, laws pertaining to the clergy, sacraments, ecclesiastical jurisdiction), the second part explains each canon with the aid of previous research literature and interpretations in order to provide a short overview of their purpose and content. The third part deals with the reception of the canons in the early Church by councils, bishops, and ecclesiastical writers, and asks what importance was attributed to the Nicene canons in various canonical sources. Finally, some desiderata for future research are discussed.

Penance was a possibility for returning heretics and for other sinners too. As is well known, the penitential system was quite different from what developed subsequently, key features being that the penance was public, marking reinsertion into the community, and that it could be done only once, though anyone could be forgiven at the point of death. Again, practical problems arose: could the clergy do penance? Could one return after penance to professions with a high risk of sin, given the unrepeatability of the ritual? Such practical problems are reflected in the early decretals.