The Roman Catholic Diocese of Constance, one of the largest dioceses of Germany, was first based in the former Roman settlement of
Vindonissa, before moving its seat to Constance in the late 6th century during the Christianization of the
Alamanni tribes around Lake Constance and the Upper Rhine. Originally subordinated to the Archdiocese of Besançon, Constance became suffragan to the
Archdiocese of Mainz in 782. A deed by Emperor
Frederick I Barbarossa in 1155 confirmed the princely status of the bishop and of his bishopric as an
Imperial Estate. The territory of the prince-bishopric contracted during the following centuries under pressure from both the
Swiss Confederacy and the
House of Habsburg. Furthermore, the city of
Constance was granted the status of a free imperial city and from then on the bishop's sovereignty in the city was restricted to a small area around the cathedral. In 1527, during the Protestant Reformation, the administrative seat of the Prince-Bishop was finally moved to
Meersburg across Lake Constance. However,
Constance fell to the Counter-Reformation promoted by the Habsburgs, who eventually abolished its status as a free imperial city and incorporated it into their
Further Austrian possessions in 1548. The huge diocese of Constance suffered heavily during the Reformation and it lost several hundred parishes, convents and other Catholic foundations which were suppressed by the various states, free imperial cities and cantons in Swabia and Switzerland that had become Protestant. In the course of the
German Mediatisation in 1803, the Prince-Bishopric was dissolved and its territory was annexed to the Margraviate of Baden. In turn, the diocese was dissolved by
Pope Pius VII in 1821 after Vicar General
Ignaz Heinrich von Wessenberg had been elected diocesan administrator upon the death of the last bishop Karl Theodor von Dalberg in 1817. While Wessenberg was supported by the government of Baden, the Pope never recognized his election on account of Wessenberg's liberal views. By a bull of 16 August 1821, the pope dissolved the diocese in order to prevent Wessenberg from becoming bishop. The area of the diocese in Baden became part of the newly established
Roman Catholic Archdiocese of Freiburg in 1827 while the Swiss areas were incorporated in the Diocese of Basel. As a result of these changes, the cantons of Obwalden and Nidwalden, parts of Uri, Glarus and Zürich were assigned provisionally to the administration of the
Diocese of Chur, an arrangement still enduring. ==List of bishops==