History.—The Diocese of Sion is the oldest in Switzerland and one of the oldest north of the Alps. At first its see was at Octodorum, now called Martinach, or Martigny. According to tradition there was a Bishop of Octodorum, named Oggerius, as early as A.D. 300. However, the first authenticated bishop is St. Theodore (d. 391), who was present at the Council of Aquileia in 381. On the spot where the Abbey of Saint-Maurice now stands he built a church in honor of St. Mauritius, martyred here about 300. He also induced the hermits of the vicinity to unite 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 Maximianus at the beginning of the fourth century. At first the diocese was a suffragan of Vienne; later it became suffragan of Tarentaise. In 580 the bishop, St. Heliodorus, transferred the see to Sion, as Octodorum was frequently endangered by the inundations of the Rhone and the Drance. There were frequent disputes with the monks of the Abbey of Saint-Maurice, who were jealously watchful that the bishops should not extend their jurisdiction over the abbey. Several of the bishops united both offices, as: Wilcharius (764-80), previously Archbishop of Vienne, from which he had been driven by the Saracens; St. Alteus, who received from the pope a Bull of exemption in favor of the monastery (780); Aimo II, son of Count Hubert of Savoy, who entertained Leo IX at Saint-Maurice in 1049.
The last king of Upper Burgundy, Rudolph III, granted the Countship of Valais to Bishop Hugo (998-1017); this union of the spiritual and secular powers made the bishop the most powerful ruler in the valley of the Upper Rhone. Taking this donation as a basis, the bishops of Sion extended their secular power, and the religious metropolis of the valley became also the political center. However, the union of the two powers was the cause of violent disputes in the following centuries. For, while the spiritual jurisdiction of the bishop extended over the whole valley of the Rhone above Lake Geneva, the Countship of Valais included only the upper part of the valley, reaching to the confluence of the Trient and the Rhone. The attempts of the bishops of Sion to carry their secular power farther down the Rhone were bitterly and successfully opposed by the abbots of Saint-Maurice, who had obtained large possessions in Lower Valais. The bishops were also opposed by the patrons of the abbey, the counts of Savoy, who used this position to increase their suzerainty over Lower Valais. The medieval bishops of Sion belonged generally to noble families of Savoy and Valais and were often drawn into the feuds of these families. Moreover the bishops were vigorously opposed by the petty feudal nobles of Valais, who, trusting to their fortified castles on rocky heights, sought to evade the supremacy of the bishop who was at the same time count and prefect of the Holy Roman Empire. Other opponents of the bishops were the flourishing peasant communities of Upper Valais, which were called later the sieben Zehnten (seven-tenths). Their struggles with Savoy forced the bishops to grant continually increasing political rights to the peasant communities. Thus Bishop William IV of Raron (1437-57) was obliged to relinquish civil and criminal jurisdiction over the sieben Zehnten by the Treaty of Naters in 1446, while a revolt of his subjects compelled Bishop Jost of Silinen (1482-96) to flee from the diocese. Walter II of Supersax (1457-82) took part in the battles of the Swiss against Charles the Bold of Burgundy and his confederate, the Duke of Savoy, and in 1475 drove the House of Savoy from Lower Valais. The most important bishop of this era was Matthew Schinner (1499-1522), a highly cultivated Humanist. Bishop Schinner, fearing that French supremacy would endanger the freedom of the Swiss, placed the military force of the diocese at the disposal of the pope and in 1510 brought about an alliance for five years between the Swiss Confederacy and the Roman Church. In return for this Julius II made the bishop a cardinal. In 1513 the bishop had succeeded in having his diocese separated from the Archdiocese of Tarentaise and placed directly under the control of the pope. The defeat of the Swiss in 1515 at the battle of Marignano, at which Schirmer himself fought, weakened his position in the diocese, and the arbitrary rule of his brothers led to a revolt of his subjects; in 1518 he was obliged to leave the diocese.
The new doctrines of the Reformation found little acceptance in Valais, although preachers were sentinto the canton from Berne, Zurich, and Basle. In 1529 Bishop Adrian I of Riedmatten (1529-48), the cathedral chapter, and the sieben Zehnten formed an alliance with the Catholic cantons of the Confederation, the purpose of which was to maintain and protect the Catholic Faith in all the territories of the allied cantons against the efforts of the Reformed cantons. On account of this alliance Valais aided in gaining the victory of the Catholics over the followers of Zwingli at Cappel in 1531; this victory saved the possessions of the Catholic Church in Switzerland. The abbots of Saint-Maurice opposed all religious innovations as energetically as did Bishops Adrian I of Riedmatten, Hildebrand of Riedmatten (1565-1604), and Adrian II of Riedmatten (1604-13), so that the whole of Valais remained Catholic. Both Adrian II and his successor Hildebrand Jost (1613-38) were again involved in disputes with the sieben Zehnten in regard to the exercise of the rights of secular supremacy. In order to put an end to these quarrels and not to endanger the Catholic Faith he relinquished in 1630 the greater part of his rights as secular suzerain, and the power of the bishop was thereafter limited almost entirely to the spiritual sphere.
The secular power of the bishops was brought to an end by the French Revolution. In 1798 Valais, after an heroic struggle against the supremacy of France, was incorporated into the Helvetian Republic, and Bishop John Anthony Blatter (1790-1817) retired to Novara. During the sway of Napoleon Valais was separated from Switzerland in 1802 as the Rhodanic Republic, and in 1810 was united with France. Most of the monasteries were suppressed. In 1814 Valais threw off French supremacy, when the Allies entered the territory; in 1815 it joined Switzerland as one of the cantons. As partial compensation for the loss of his secular power the bishop received a post of honor in the Diet of the canton and the right to four votes. Disputes often arose as the Constitution of 1815 of the canton gave Upper Valais political predominance in the cantonal government, notwithstanding the fact that its population was smaller than that of Lower Valais. This led in 1840 to a civil war with Lower Valais, where the “Young Swiss” party, hostile to the Church, were in control. The party friendly to the Church conquered, it is true, and the influence of the Church over teaching was, at first, preserved, but on account of the defeat of the Sonderbund, with which Valais had united, a radical Government gained control in 1847. The new administration at once showed itself unfriendly to the Church, secularized many church landed properties, and wrung large sums of money from the bishop and monasteries. When in 1856 the moderate party gained the cantonal election, negotiations were begun with Bishop Peter Joseph von Preux (1843-75), and friendly relations were restored between the diocese and the canton. In 1880 the two powers came to an agreement as to the lands taken from the Church in 1848; these, so far as they had not been sold, were given back for their original uses. Since then the bishop and the Government have been on friendly terms. The new Constitution of 1907 declares the Catholic religion to be the religion of the canton, and forbids any union of spiritual and secular functions. The ordinances regulating the election of a bishop which have been in existence from early times, at least, contradict this (see below). The present bishop is Julius Mauritius Abbet, b. September 12, 1845, appointed auxiliary bishop cum jure successions October 1, 1895, succeeded to the see February 26, 1901.
Statistics.—The boundaries of the Diocese of Valais have hardly been changed since it was founded; the diocese includes the Upper Rhone Valley, that is, the Canton of Valais, with exception of the exempt Abbey of Saint-Maurice, and of the Catholic inhabitants of Saint-Gingolph, who belong to the French Diocese of Annecy; it also includes the parishes of Bex and Aigle that belong to the Canton of Vaud. In 1911 the diocese had 11 deaneries, 125 parishes, 70 chaplaincies, 208 secular priests, 135 regular priests and professed, about 120,000 Catholics. Nearly 30 per cent of the population of the diocese speak German, and nearly 65 per cent French; the language of the rest of the population is Italian. The bishop is elected by the denominationally mixed Great Council from a list of four candidates presented by the cathedral chapter, and the election is laid before the pope for confirmation. The cathedral chapter consists of ten canons; in addition five rectors are included among the cathedral clergy. The clergy are trained at a seminary for priests at Sion that has six ecclesiastical professors and twelve resident students; there are also six theological students studying at the University of Innsbruck. The religious orders of men in the diocese are: Augustinian Canons, with houses on the Great St. Bernard, the Simplon, and at Martigny, containing altogether 45 priests, 6 professed and 7 lay brothers; Capuchins, at Sion and Saint-Maurice, numbering 22 priests, 6 students of theology, and 9 lay brothers. The exempt abbey of Augustinian Canons at Saint-Maurice contains 46 priests, 9 professed and lay brothers. The orders and congregations of nuns in the diocese are: Bernardines at Colombay; Hospital Sisters at Sion; Sisters of St. Vincent de Paul at Saint-Maurice; Franciscan Nuns, at the same place; Sisters of Charity of the Holy Cross at Sion, Leuk, and Leukerbad; Ursuline Nuns at Sion and Brieg.