The sources of canon law date back to the origins of the Church and include the Holy Scriptures, the works of the Church Fathers, moral principles and philosophical meditations. With the birth of particular Churches and various rites and liturgies, early forms of canonical legislation are developed, and within it, numerous institutions of Roman law are adopted. Starting from the sixth century major ecumenical councils fix the dogmas of the Christian faith as well as a number of legal rules, then gathered in council decisions. With the multiplication of legal and disciplinary disputes between the various churches, or between members of the same church, need arises to resort to the Bishop of Rome to settle the thorniest issues.
Thus the papal Decretales and Collectiones are born (the Collectio Dionysian between 498 and 514, the Collectio Isidoriana between 629 and 636, the Collectio Hadriana in 774). Under the pressure of barbarian invasions the need to give a solid legal basis to the action of the church becomes increasingly urgent.
In the twelfth century, more precisely from around 1140, the Camaldoli-based monk Gratian undertakes the first ever work of rearrangement of the canonical texts: he gathers a vast collection of sources (decrees, conciliar canons, patristic passages, the Roman Lex Visigothorum, Carolingian capitularies) and he elaborates numerous interpretations able to integrate and reconcile the conflicting norms. Such a work, with the significant title of Concordia discordantium canonum, together with the subsequent collections of pontifical Decretales (the Liber Extra, the Liber Sextus, the Clementinae, the Extravagantes Iohannis XXII and Extravagantes communes), will become part of the Corpus Iuris Canonici, and all together they will remain a source of canon law until the promulgation of the Code of 1917.
With the flourishing of the Italian universities and the legal doctrine, the work of Gratian is the subject of intense teaching and scientific activity that takes place with the same methodology used for the Justinian's Corpus: glosses and marginal comments become part of the text and are published in printed form during the XVI century. Summae, systematic treaties of canon law and many commentaries are subsequently produced. The Protestant Reformation profoundly affected the structure of the Church, which, with the Council of Trento, fixed doctrinal and disciplinary rules. These latter will, in turn, contribute in a decisive way to the legal aspect of the ecclesiastical organization.
