Decretals () are letters of a pope that formulate decisions in ecclesiastical law of the Catholic Church. They are generally given in answer to consultations but are sometimes given due to the initiative of the pope himself. These furnish, with the canons of the councils, the chief source of the legislation of the church, and formed the greater part of the Corpus Iuris Canonici before they were formally replaced by the Codex Iuris Canonici of 1917. However, Cardinal Pietro Gasparri led the papal commission for the revision of canon law and later on published a guide to the fontes (sources) used in the 1917 code. Many canons in this code can easily be retraced in their relationship to and dependency on medieval decretals as well as Roman law. In themselves, the medieval decretals form a very special source which throws light on medieval conflicts and the approaches to their solution. They are sometimes concerned with very important issues touching on many aspects of medieval life, for example: marriage or legal procedure. Definition and early history In a wider sense, the Latin term decretalis (in full: epistola decretalis) signifies a pontifical letter containing a decretum, or pontifical decision. In a narrower sense, it denotes a decision on a matter of discipline. In the strictest sense of the word, it means a papal rescript (rescriptum), an answer of the pope when he has been appealed to or his advice has been sought on a matter of discipline. Papal decretals are therefore not necessarily general laws of the church, but frequently the pope ordered the recipient of his letter to communicate the papal answer to the ecclesiastical authorities of the district to which he belonged; and it was their duty then to act in conformity with that decree when analogous cases arose. It is generally stated that the most ancient decretal is the letter of Pope Siricius (384–398) to Himerius, Bishop of Tarragona in Spain, dating from 385; but it would seem that the document of the fourth century known as Canones Romanorum ad Gallos episcopos is simply an epistola decretalis of his predecessor, Pope Damasus (366–384), addressed to the bishops of Gaul (Babut. La plus ancienne décrétale. Paris, 1904). The decretals ought to be carefully distinguished from the canons of the councils; from the epistol dogmatic (the pontifical documents touching on Catholic doctrine), from the constitutiones, or pontifical documents given motu proprio