IN PARTIBUS INFIDELIUM. - Until 1882 those bishops were called "episcopi i. p. i." or simply "in partibus" who, though duly nominated and consecrated, were not given by the pope a definite group of faithful living in a determined territory (a diocese) to govern, 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 and not of jurisdiction.
The origin of such a designation goes back to the end of the 13th century or the beginning of the 14th century and may be considered as definitively accepted in the following century. It was, in fact, in the wake of the Crusades and of the establishment of a Latin empire at Constantinople (A.D. 1204), that many sees were erected alongside Churches of the Eastern rite, episcopal Latin sees, 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 the Muslims, having succeeded in reconquering the lost territories, abolished and destroyed the civil and ecclesiastical order established by the Crusaders, and the bishoprics ceased in fact to exist. The Latin bishops who fled adapted themselves to performing service and to helping the brethren of the regions immune from Turkish rule, which had given them hospitality. It must be noted, however, that the forced suppression of many Latin dioceses of the Levant did not interrupt the continuity of the hierarchical succession (not all were overwhelmed simultaneously: those in the Venetian domains lasted longer). When the pastors who had governed them passed away, others were appointed, and not always in the regular forms, who, inheriting the mere title, received the fullness of the priesthood. The Holy See soon intervened to reserve to itself the appointments to these nominal sees, whose generic designation, for several centuries, was "i. p. i."
Later, owing to the decline of the Turkish Empire, the territory of many of these sees returned to being inhabited in the majority by Christian populations of the Eastern rite, separated from the Catholic Church, but not infidels in the sense given to the word. The appellation therefore of sees "i. p. i." was in several cases no longer appropriate.
Therefore Leo XIII, by means of a decree of the Sacred Congregation of Propaganda Fide, dated 3 March 1882 (Collectanea Sacrae Congregationis de Propaganda Fide, II, Rome 1907, n. 1565, p. 157), abolished the formula "episcopi i. p. i." and established that it be replaced with that of "titular bishops," in order to distinguish them from residential bishops. Titular bishops enjoy, with few exceptions, the privileges and honors of residential bishops (can. 439 § 1).
Bibliography5 works
Pompeo Borgna