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 troops and Sion was plundered. Under the Helvetic Republic, Sion was source of conflict between supporters and opponents of the new regime. In May 1799 counter revolutionary forces from Upper Valais looted the city again. In order to ensure peace in the Valais, the French General Louis Marie Turreau de Garambouville occupied Sion in 1801 and in 1802 Napoleon Bonaparte declared the independent Rhodanic Republic. It then remained independent until 1810 when it was annexed into France as the département of Simplon. Between 1798 and 1801 the representative of the Helvetic government resided in Sion. Under the French occupation, Joseph