«IN PARTIBUS INFIDELIUM». — Until 1882 bishops were called «episcopi i. p. i.» or simply «in partibus» who, though duly appointed and consecrated, were not given charge of a defined body of the faithful living in a specific territory (a diocese) but were assigned, as their episcopal title, one of those ancient episcopal sees of the Near East, destroyed by the Ottoman invasion, in which they could not reside. They were therefore bishops with the power of order but not of jurisdiction.
The origin of this designation goes back to the end of the 13th or the beginning of the 14th century and may be considered as definitively admitted in the following century. It was, in fact, as a result of the Crusades and the establishment of a Latin empire at Constantinople (A.D. 1204), that, alongside Churches of the Eastern rite, many Latin sees were created for the spiritual care of Latin Catholics in the lands of the East occupied by Western princes or subject to their influence: Asia Minor, Egypt, Palestine, the Aegean Islands and the Balkan Peninsula. Some centuries later, when the Muslims had succeeded in reconquering the lost territories, they abolished and destroyed the civil and ecclesiastical organization established by the Crusaders, and the bishops ceased in fact to exist. The refugee Latin bishops adapted themselves to serving and assisting their brethren in regions immune from Turkish rule, which had given them shelter. It must however be noted that the forcible suppression of many Latin dioceses in the Levant did not interrupt the continuity of their hierarchical succession (not all were overwhelmed simultaneously: those in Venetian dominions lasted longer). When the pastors who had governed them were no longer available, others were appointed, not always in regular form, who, inheriting only the bare title, received the fullness of the priesthood. The Holy See soon intervened to reserve for itself the revenues of these titular sees, whose generic appellation, for several centuries, was «i. p. i.».
Later, with the decline of the Turkish empire, the territory of many of these sees again became inhabited in the majority by Christian populations of the Eastern rite, separated from the Catholic Church but not infidel in the sense given to the word. The appellation therefore of sees «i. p. i.» was in many cases no longer appropriate.
Hence Leo XIII, by a decree of the Sacred Congregation of Propaganda Fide, dated March 1852 (Collectanea Sacrae Congregationis de Propaganda Fide, II, Rome 1907, no. 1565, p. 157), abolished the formula «episcopi i. p. i.» and laid down that it should be replaced by that of «titular bishops», to distinguish them from residential bishops. Titular bishops, with few exceptions, enjoy the privileges and honours of residential bishops (can. 439 § 1).