Of all the forms of representation available for use by rulers and their subjects in their relations with the pope and the Roman curia during the early modern period, that of the cardinal protectors of the crowns is the most novel and the least known. Studies devoted to the institution have been few and published almost exclusively by German-speaking authors. In the most comprehensive synthesis of the subject to date, published in 1938, the Austrian historian Josef Wodka focused essentially on the origins of the institution, from the 1420s to the early sixteenth century. In the seventeenth century, when authors of treatises on the Roman curia or on the rank of cardinal mentioned the protectorships granted to cardinals, which some of them, like Giovanni Battista de Luca, described as posti cardinalizi, they usually divided their account into two or three parts, dealing in turn with the protectorships of religious orders, that of Roman religious establishments and bodies, and finally that of the European states.

It was in the thirteenth century that the first protectorships were given to cardinals with a view to safeguarding the interests of religious orders. The regula bullata which organized the Order of St Francis of Assisi in 1223 defined, among other things, the role assigned to Cardinal Ugolino, Bishop of Ostia and the future Pope Gregory IX (1227–41).