Papal letters constituted an integral element of the institution of the crusade and are among the most important sources for the history of the movement. Although often referred to as crusade bulls, not all papal letters concerned with the crusade were technically speaking bulls, which constitute a special type of papal letter with a lead seal (Lat. litterae apostolicae sub plumbo). More recently historians have preferred the neutral term papal letters, thus adopting the medieval terminology, which generally designated papal correspondence as litterae apostolicae (apostolic letters). These included various types of letters referred to as privileges, bulls, or different classes of letters. Especially for the period after 1200, when part of the outgoing correspondence was registered at the Curia, copies of papal letters dealing with various aspects of the crusades have survived in large numbers. Such letters were also inserted in narrative accounts and letter collections and are preserved as originals in many archives throughout Europe.
Papal letters were instruments of communication and also legal documents, which the papacy used to initiate, regulate, and control the crusades. They were used to announce crusades, set out terms of participation, authorize the spiritual and temporal privileges accorded to crusaders and their dependants, proclaim taxes and other means of financing crusades, and deal with any organizational or legal matter arising before, during, or after a crusade. Popes not only sent letters to individuals involved in expeditions, or to leading exponents expected to become involved; they also addressed bishops, local clergy, and members of religious orders who acted as agents for the popes, communicating matters pertaining to the crusades to a wider public. Most important among these were the general letters (encyclicals), usually addressed to all Christian people, proclaiming a new crusade. These were sent to the actual or potential secular leaders of the crusade as well as to clerics who were commissioned to preach the cross. Papal legates, bishops, and the heads of the mendicant orders commissioned and passed on copies of these letters to individual crusade preachers. With the introduction of printing around the middle of the fifteenth century, copies of papal letters were also printed to facilitate distribution.
The contents of the papal letters announcing a crusade gave preachers the necessary practical information, such as dates, location, and rationale, for promoting a particular crusade expedition. In order to ensure the accurate transmission of the papal message, popes sometimes demanded that their letters be read aloud by preachers during propaganda events. Extant copies of such letters with a vernacular translation on the back show that these orders were taken seriously. The presentation of a copy of the papal letter in public also served as a way of establishing crusade preachers’ credentials as papal agents. At times bishops formally endorsed such copies in order to strengthen propagandists’ authority and make unauthorized crusade preaching more difficult. Apart from such general letters, the popes sent out letters giving instructions concerning individual matters, answering queries from crusaders or those organizing the crusade, effecting changes to particular commissions, and clearing up points that had led to conflicts of interest among the participants. Thus papal letters were a means of adjusting propaganda strategies, redistributing funds, and monitoring the formation of crusade armies once a crusade had been declared. Popes usually also stayed in regular contact by exchange of letters with the leaders of a crusade expedition once an army was under way, thus keeping themselves informed of its progress.
The first papal letters concerning the crusades were written by Urban II and dealt with various issues arising during the preparations for the First Crusade (1096-1099). The earliest known general letter (which has not survived) was issued by Calixtus II in 1122 to announce a new crusade expedition to the Holy Land. A number of general letters published during the twelfth century were pivotal in defining the crusades in terms of ideology and organization, leading toward a fullblown elaboration of the institution of the crusade and the crusade movement at the beginning of the thirteenth century. Among these were Eugenius III’s Quantum praedecessores of 1145/1146, which announced the Second Crusade (11471149); Gregory VIII’s Audita tremendiof 1187, responding to the battle of Hattin and initiating the Third Crusade (1189-1192); and Innocent III’s Post miserabile of 1198, which marked the beginning of the Fourth Crusade (1202-1204). In 1213 Pope Innocent III issued Quia maior, the most elaborate and most comprehensive general letter yet, announcing the Fifth Crusade (1217-1221). In this he regulated a whole range of issues, from different forms of participation and mechanisms for raising funds to the issue of vow redemptions and liturgy, thus presenting a model for future general letters. Quia maior was the basis for Ad liberandam, the constitution dealing with the crusade to the Holy Land incorporated in the acts of the Fourth Lateran Council of 1215. In turn, Ad liberandam formed the basis for the majority of calls for crusades well into the fourteenth century. During the thirteenth century, copies of this letter were at times issued to crusade preachers alongside other papal letters to serve as a reference for the legal rules concerning vows and indulgences.
The papal crusade letter concerning the crusades in the Iberian Peninsula, known in Spanish as bula de la cruzada (“crusade bull”), has its own history. It originally confirmed the indulgences granted by the pope in the context of the crusade movement; after the end of military crusade ventures, it became an instrument for raising money for various other matters by offering indulgences in return for pious donations, and was only abolished in 1966.