Roman Catholic Diocese of Sion

Diocese of Sion Dioecesis Sedunensis Bistum Sitten (de) Évêché de Sion (fr)
The Cathedral of Notre Dame du Glarier
Location
Country	Switzerland
Metropolitan	Immediately Subject to the Holy See
Statistics
Area	5,589 km2 (2,158 sq mi)
Population - Total - Catholics	(as of 2010) 309,202 235,735 (76.2%)
Parishes	158
Information
Denomination	Roman Catholic
Rite	Latin
Established	4th century
Cathedral	Cathédrale Notre-Dame du Glarier
Current leadership
Pope	Francis
Bishop	Jean-Marie Lovey
Emeritus Bishops	Norbert Brunner Cardinal Henri Schwery
Map
Map of the modern diocese of Sion within Switzerland
Website
Website of the Diocese

Prince-Bishopric of Sion or Prince-Bishopric of Wallis
Fürstbistum Sitten (de) Prince-Évêché de Sion (fr) Dioecesis Sedunensis (la)
State of the Holy Roman Empire
999 – 1798
Flag Coat of arms
Anthem Notre Valais (, )
Map of Switzerland in 1378, showing the Bishopric labelled Valais
Capital		Sion
Languages		French, Walser German
Religion		Roman Catholic
Government
Bishop
•	before 381–391	St Theodore of Octodurus
Prince-Bishop
•	998–1017	Hugo, Count of Valais (first Prince-Bishop)
•	1613–38	Hildebrand II Jost (last de facto Prince-Bishop)
•	1790–1807	Joseph-Antoine Blatter (last de jure Prince-Bishop)
Historical era		Middle Ages
•	Bishopric founded	before 381 999
•	See moved to Sion	589
•	Bequeathed county     of Valais	around 999
•	Became associate     of Old Swiss Confed.	March 12, 1529
•	Became republic     under guidance of     the Bishop	1628
•	Foundation of     Helvetic Republic	April 12, 1798 1798
•	Entered Swiss Confed.     as canton of Valais	August 4, 1815
Preceded by Succeeded by Kingdom of Upper Burgundy Sieben Zenden Helvetic Republic

The Diocese of Sion (Latin: Dioecesis Sedunensis, French: Évêché de Sion, German: Bistum Sitten) is a Roman Catholic ecclesiastical territory in the canton of Valais, Switzerland. It is the oldest bishopric in the country and one of the oldest north of the Alps. The history of the Bishops of Sion, of the Abbey of St. Maurice of Valais as a whole are inextricably intertwined.

The see was established at Octodurum, now called Martigny, the capital of the Roman province of Alpes Poeninae. The first authentically historical bishop was Saint Theodore/Theodolus (died in 391), who was present at the Council of Aquileia in 381. He founded the Abbey of Saint-Maurice, with a small church in honor of Saint Maurice, martyred there c. 300, when he united the local hermits in a common life, thus beginning the Abbey of Saint-Maurice, the oldest north of the Alps. Theodore rebuilt the church at Sion, which had been destroyed by Emperor Maximinus at the beginning of the 4th century. At first the new diocese was a suffragan of the archdiocese of Vienne; later it became suffragan of Tarentaise.

In 589 the bishop, St. Heliodorus, transferred the see to Sion, leaving the low-lying, flood-prone site of Octodurum, where the Drance joins the Rhone. Though frequently the early bishops were also abbots of Saint-Maurice, the monastic community was jealously watchful that the bishops should not extend their jurisdiction over the abbey. Several of the bishops united both offices: Wilcharius (764-780), previously Archbishop of Vienne, whence he had been driven by the Moors; St. Alteus, who received from the pope a bull of exemption in favor of the monastery (780); Aimo II, son of Count Humbert I of Savoy, who entertained Leo IX at Saint-Maurice in 1049.