Since the thirteenth century it has been customary for the pope to assign to a particular prelate, and since 1420 to one with the rank of cardinal, a special responsibility in the Roman Curia for the interests of a given religious order or institute, confraternity, church, college, city, nation, etc.
Nearly every provincial city had its patronus, or procurator, in imperial Rome, usually a Roman patrician or eques, and such persons were held in high esteem.
Such a cardinal protector had the right to place his coat-of-arms on the church or main edifice of the institute, or on the municipal palace of the city in question.
While Sixtus IV and Julius II defined more particularly the limits of the office, Pope Innocent XII (1691–1700) must be credited with a lasting regulation of the duties and rights of a cardinal protector.
[8] And in March 1436, the council duly decreed: "And as the cardinals should assist him who is the common father of all [the pope], it is highly improper for them to make distinctions between persons or to become their advocates.
[11] On 5 May 1514, in the ninth session of the Lateran Council, Pope Leo X promulgated his bull, "Supernae dispositionis", extensively reforming the Roman Curia.
Leo points out that cardinals give assistance to the common Father of all Christian faithful, and that advocates of individuals are an annoyance.
He therefore orders that cardinals should not take up any position of partiality, either of princes or communities, or of other people against some one person, nor should they become promoters or defenders unless some point of justice or equity demands it, or their own dignity and condition requires it.