A titular see in the Roman Catholic Church is a Diocese or Archdiocese that now exists in title only. Until 1882, such titular sees, were distinguished by the Latin phrase in partibus infidelium ("in the territory of the infidels") or more often simply in partibus. It is led by a titular bishop or Archbishop, a bishop who is not a diocesan ordinary but either an official of the Holy See, an auxiliary bishop, or the head of a jurisdiction that is equivalent to a diocese under canon law. Bishops who do not have proper authority over an existing diocese are normally given a titular see by the Pope. At one time coadjutor bishops and archbishops were given titular sees — however now they are given title to the diocese or archdiocese that they will oversee as coadjutor. Retired Bishops and Archbishops were also given titular sees, however the common practice now is to name them Bishop or Archbishop Emeritus of the see they retired from.
The Roman Curia maintains a regular position on titular sees. It states:
It is the custom of the apostolic see to confer on these bishops the title of one of those churches which in days past flourished with the splendor of virtue and the progress of religion, even though as a result of the changes and ravages of time they may now have lost their ancient resplendent glory.While the Vatican hopes that titular sees will one day become active dioceses once again, it realizes in most cases the chances of that happening are low. Some titular sees appear also to remain vacant for oecumenical reasons (e.g. a number of those in the immediate vicinity of Greek Orthodox patriarchates).
In Partibus Infidelium (often shortened to in partibus, or abbreviated as i.p.i.), is a Latin phrase meaning "in the lands of unbelievers," words once added to the name of the see conferred on non-residential or titular Roman Catholic bishops, for example: "John Doe, Bishop of Tyre (Lebanon) in partibus infidelium".
During the historical expansion of Christianity, the Roman Catholic Church expanded its realm. However, in some areas of the world where the religion once flourished, the presence of the Roman Catholic Church has now diminished or disappeared. Local churches split off from the larger Church while other regions were converted to Islam. Reorganizations would sometimes lead to dioceses being absorbed into one or more other dioceses. At times the see cities of dioceses were relocated to other cities, and the diocese in question was renamed. The Roman Catholic Church adopted the practice of assigning bishops to titular sees as a way of remembering those dioceses.
Formerly, when bishops were forced to flee from their see, they were welcomed by other Churches, while preserving their titles and their rights to their own dioceses. They were even entrusted with the administration of vacant sees. Thus, we find St. Gregory appointing John, Bishop of Alessio, who had been expelled by his enemies, to the See of Squilace (cap. Pastoralis, xliii, caus. vii, q. 1). In later days it was deemed fitting to preserve the memory of ancient Christian Churches that had fallen into the hands of other religions; this was done by giving their names to auxiliary bishops or bishops in missionary countries.
An interesting example of an enduring 'in Partibus' bishopric is that of the Bishop of Bethlehem. In 1168, the crusading William IV, Count of Nevers had promised the Bishop of Bethlehem that if Bethlehem should fall under Muslim control, he would welcome either him or his successors in the small town of Clamecy in the present day Burgundy, France. After the capture of Bethlehem by Saladin in 1187, the bequest of the by then deceased Count was honoured and the Bishop of Bethlehem duly took up residence in the hospital of Panthenor, Clamecy in 1223. Clamecy remained the continuous 'in partibus infidelium' seat of the Bishopric of Bethlehem for almost 600 years, until the French Revolution in 1789..
Prospero Fagnani (in cap. Episcopalia, i, De privilegiis) says that the regular appointment of titular bishops dates back only to the time of the Fifth Lateran Council under Leo X (Session IX); cardinals alone were authorized to ask for them for the dioceses. St. Pius V extended the privilege to the sees in which it was customary to have auxiliary bishops. Since then the practice became more widespread. The Sacred Congregation of the Propaganda, by its circular letter of 3 March, 1882, abolished the expression in partibus infidelium; the present custom is to join to the name of the see that of the district to which it formerly belonged, e.g. "Johannes Doe, Archiepiscopus Corinthius in Achaiâ," or else merely to say "titular bishop".
Occasionally, the transfer of a diocesan bishop to a titular see has been used by the Holy See to strip of his responsibilities a bishop whose behavior it disapproved of. For instance, in 1995, Bishop Jacques Gaillot, known for his activism on Catholic-sensitive social and political topics, was transferred from the Diocese of Évreux in France to Partenia, a titular see in Algeria.
The granting of titular sees is occasionally practiced in the Eastern Orthodox Church, for example, to avoid causing offense or confusion when an Orthodox bishop serves a place which is also the see of a non-Orthodox bishop (e.g. the Orthodox bishop in Oxford, England, is titled Bishop of Diokleia).