Chronology of Catholic Dioceses:Notes on the diocese of Sion, c. 300-400

The diocese of Sion is the oldest in Switzerland and one of the oldest north of the Alps. The see was first established at Octodorum (now Martinach/Martigny). Tradition mentions a Bishop Oggerius of Octodorum c. 300, but the first certain mention of the diocese is from 381, when Bishop St. Theodore of Octodorum was present at the council of Aquileia. It was first a suffragan of Vienne, and was later transferred to the jurisdiction of Tarentaise.

In 589, the see was transferred to Sion because Octodorum was threatened by the flooding of the Rivers Rhone and Drance.

From 998, the bishops of Sion held secular power as counts of Valais, a title transferred by Rudolph III, last king of Upper Burgundy. Their secular power was ended by the French Revolution in 1798, when Valais was incorporated in the Helvetian Republic to protect it from French expansion attempts.

(Source: Catholic Encyclopedia, http://www.newadvent.org/cathen/14014d.htm)

-CNy