SION (SITTEN), DIOCESE OF. – A city and diocese, capital of the canton of Valais in Switzerland. It covers an area of 5,235 sq. km with a population of 150,000, of whom 145,000 are Catholic; it has 145 parishes served by 251 diocesan priests and 148 regular clergy; there are 18 male and 33 female religious communities (Ann. Pont. 1953, p. 402).
Its origins date back to the early centuries of Christianity and it was called "Sedunum." The Valais was conquered by Augustus around 8 BC. By 377 it was certainly Christian, as evidenced by an ancient inscription from that period bearing the monogram of Christ. The present diocese covers the entire territory of the canton, except for five communes, and its boundaries have changed little over the centuries.
The first recorded bishop is Theodore, "episcopus Octodurensis," as he signed himself at the Council of Aquileia (381) and the Council of Milan (390); he established his see at Octodurum (Martigny); he founded the church of St. Maurice in honor of the martyrs of the Theban Legion at Agaunum (v.). The bishops Salvo and Protasio followed; Constantius attended the Council of Épao (517) and Rufus those of Orléans (541 and 549); Heliodorus probably moved the see to Sion around 585; it is certain, however, that Leudemund definitively established it there in 613. Protasio attended the Council of Chalon-sur-Saône (650); Walcher, already metropolitan of Vienne, was both bishop of Sion and abbot of St. Maurice: in 771 he paid homage to Charlemagne; his funerary inscription is preserved (P. Bourban, L'archevêque et Vultchaire et son inscription funéraire, in Comptes rendus du IV Congrès scientifique internationale des catholiques, Fribourg 1898, 10e sect., pp. 19-35).
In the 4th century, Sion was under the metropolitan jurisdiction of Milan, then around the mid-5th century it passed under that of Vienne, and by the end of the 8th century under that of Tarentaise. The earliest lists of bishops of Sion date from the 16th century. The first seven resided at Octodurum, from Theodore I (380–91) to Agricola (565); the remaining 76 were at Sion, from Heliodorus (585) to the last, Abp. Bieler (1919–52). The height of the episcopal power in Sion extended from 999 to 1032, when the bishop was count and imperial representative, minister of justice of the army, and secular prince: the last bishop to bear this title was Bp. P. J. de Proux (1843–75): *Sacri Romani Imperii princeps*. The most towering figure in the history of
