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
Lauda Sion Roman Catholic Church in transubstantiation, that is, that the bread and wine truly become the Body and Blood of Christ when consecrated by a validly-ordained priest or bishop during the Mass. "Lauda Sion" is one of only four medieval Sequences which were preserved in the "Missale Romanum" published in 1570 following the Council of Trent (1545–1563)—the others being Victimae paschali laudes (Easter), Veni Sancte Spiritus (Pentecost), and Dies Irae (Requiem Masses). (A fifth, Stabat Mater, would later be added in 1727.) Before Trent, many feasts had their own sequences. The "Lauda Sion" is still sung today, though its use is