Roman Catholic Diocese of Sion Roman Catholic Diocese of Sion The Diocese of Sion (, , ) 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
Sion, Switzerland regulations. Sion was now a city with city walls, documented freedoms and the market right. From the middle of the 14th century to 1475, the history of Sion was filled with wars and destruction. Bishop Witschard Tavel tried to reduce the privileges of the cathedral collegiate chapter and the citizenry with the support of the Count of Savoy. In 1352, Sion was conquered, pillaged and plundered by an army from Savoy. In 1373, the Bishop bought back the majority of the fief of Sion from the de Greysier family. Majorie Castle became the Bishop's residence and the "maior" was now