Tourbillon Castle  Tourbillon Castle (French: "Château de Tourbillon") is a castle in Sion in the canton of Valais in Switzerland. It is situated on a hill and faces the Basilique de Valère, located on the opposite hill. The castle was ruined in a fire in 1788. It is a Swiss heritage site of national significance. The Diocese of Sion was founded in Octodurum, now called Martigny in the early 4th century. In 589 the bishop, St. Heliodorus, transferred the see to Sion, as Octodurum was frequently endangered by the inundations of the Rhone and the Drance. Very little is known about the early Bishops and the early churches in Sion. However, in the late 10th century the last King of Upper Burgundy Rudolph III, granted the County of Valais to Bishop Hugo (998-1017). The combination of spiritual and secular power made the Prince-Bishops the most powerful nobles in the Upper Rhone valley. Sion became the political and religious center of the region. By the 12th century they began building impressive churches and castles in Sion to represent their power and administer their estates. Valère, as the residence of the cathedral chapter in Sion, was one-third of the administrative center of the powerful Diocese of Sion. In the 12th century the Cathedral Notre Dame de Sion (du Glarier) was built in the town below Valère hill. Glarier Cathedral became the seat of the Diocese of Sion, while the Prince-Bishop of Sion lived in the castle. Tourbillon Castle was built sometime between 1290 and 1308 by the Bishop of Sion, Boniface de Challant, as his principal residence. After Boniface died in 1308, his successor Aymon II de Châtillon probably finished the castle. In 1352 the Upper Valais revolted against Bishop Guichard Tavel. Led by Peter de la Tour, in November of that year, they marched on Sion, burned the town and unsuccessfully besieged the castle. In 1373, the Prince-Bishop bought Majorie Castle and moved his residence off the rocky spire. However, Bishop Tavel was not able to enjoy his new palace for long. In 1375 he was captured and murdered by rebels led by Peter's son, Anton de la Tour, in 1375. Tourbillon became the Prince-Bishop's summer residence and remained a visible symbol of secular and ecclesiastical power.