The individual graves changed at the beginning of the 3rd millennium BC in large, dry stone wall communal tombs (such as the Dolmen of Le Petit-Chasseur).

[citation needed] The Roman settlement stretched mainly from what is now St. Theodul, between the Sionne and to the west side of the hill, Valeria.

Near La Sitterie, Sous-le-Scex and in the upper part of the Avenue du Petit Chasseur, portions of several villae suburbanae were found.

Grave stelae attest to the presence of duumviri (magistrates of the civitas), of flamines (priests of the imperial cult), a Roman knight and a former consul in the town.

In the 4th century praesides (provincial governors) are mentioned living in Sedunum, including a man named Pontius Asclepiodotus, who rebuilt an imperial building and, according to an inscription, converted to Christianity in 377.

[10] In 589 the bishop, St. Heliodorus, transferred the see to Sion, leaving the low-lying, flood-prone site of Octodurum, where the Drance joins the Rhône.

Several of the bishops united both offices: Wilcharius (764–780), previously archbishop of Vienne, whence he had been driven by the Moors; Saint Alteus, who received from the pope a bull of exemption in favor of the abbey (780); Aimo II, son of Count Humbert I of Savoy, who entertained Leo IX at Saint-Maurice in 1049.

The residents of Sion were ruled by three appointees of the bishop, the maior, the vice dominus or Viztum and the salterus.

[7] As a result of the decline of the feudal social order and thanks to privileges and concessions granted by the bishop, the citizens of Sion had a limited independence in the Middle Ages.

A contract between Bishop Kuno and his maior William of Turn from 1179, is seen as the first step in the creation of an independent city government.

An agreement between the bishop, the collegiate church of St. Viztums and William of Turn in 1217 is the first written charter of freedom for the city.

In the same year, Emperor Louis the Bavarian raised Sion to a free imperial city and collected the surrounding lands into a barony.

Bishop Witschard Tavel tried to reduce the privileges of the cathedral collegiate chapter and the citizenry with the support of the Count of Savoy.

In 1433, Bishop Andreas dei Benzi approved a strict set of regulations concerning the granting of citizenship rights to applicants.

[7] In the 16th century, due to a strong immigration from the German-speaking Upper Valais, Sion/Sitten became almost totally German speaking.

As the civic community gradually began to organize, they were no longer willing to automatically grant every new arrival the same rights as citizens.

The permanent residents were mainly workers, craftsmen (often originating from the Swiss Confederation and the Germanies) and traders (mostly from Savoy and northern Italy).

The station at Sion included a Sust or warehouse that also provided additional animals to help haul wagons over the pass.

In the 17th century, citizens claimed the right to choose their parish priest, over objections of the ecclesiastical authorities.

[7] In the second half of the 16th century a large Protestant community grew in Sion under the leadership of renowned burghers, who had learned of the new doctrine while students in Bern, Basel, Zürich, Lausanne or Geneva.

The Counter-Reformation, led by the Capuchin friars of Savoy and the Jesuits destroyed the last hopes of the Protestants to establish a foothold in the cathedral town.

In order to ensure peace in the Valais, the French General Louis Marie Turreau de Garambouville occupied Sion in 1801 and in 1802 Napoleon Bonaparte declared the independent Rhodanic Republic.

Under the French occupation, Joseph du Fay de Lavallaz was appointed by the emperor to be the mayor of the district of Sion.

Archaeologists found six aligned standing stones in La Petit district in Sion in July 2019.

[11] "This discovery is of prime importance to help us understand social rituals at the end of the Neolithic period (around 2,500BC) in central Europe," was announced from the canton of Valais.

The largest of the stones assumed to be a male figure wearing geometrically decorated clothes with a sun-like motif around his face is about two tonnes.

Over the same time period, the amount of recreational space in the municipality increased by 66 ha (160 acres) and is now about 4.47% of the total area.

[15][16] The Medieval chroniclers report the occurrence of severe flood events, and during the Little Ice Age (or LIA, 1350–1850 AD) the Upper Rhône had certainly a torrential regime as other rivers in the Western Alps.

Sion is the third largest wine making region in Switzerland, however, the valuable agricultural land and vineyards are undergoing constant regression due to the process of urbanisation.

The secular buildings include the Archives de l’État du Valais, the Archives and Museum of the Bishop of Sion and the cathedral, the town hall (with its astronomical clock), Majorie Castle, La Majorie on Rue des Châteaux 19, Le Vidomnat on Place de la Majorie 15, the Maison Supersaxo, the Médiathèque Valais Sion, the Cantonal Fine Arts and History Museums and the ruins of Tourbillon Castle.