Solothurn (fr. Soleure, de. Solothurn, it. Soletta, rus. Золотурн) received its name from Salodurum, a Roman-era settlement founded in the area.
The Roman settlement was built around AD 15-25 possibly as a station on the road from Aventicum to Augusta Raurica or Vindonissa. A small vicus or settlement quickly developed around the castrum. Solothurn is first mentioned in 219 as vico salod[uro] on the so-called Eponastein.

By the middle of the 5th Century, St. Eucherius of Lyon mentions the martyrdom of St. Ursus and St. Victor in Solothurn. About 500 AD, the Burgundian Princess Sedeleuba took the bones of St. Victor to Geneva, while the bones of St. Ursus remained in Solothurn. St. Ursus was often depicted on the Solothurn medieval coins.

During the Early Middle Ages, Solothurn was part of the Kingdom of Lotharingia (Lorraine). After the collapse of Lotharingia, it became part of the Second Kingdom of Burgundy. In 1033, the Kingdom of Burgundy became part of the Holy Roman Empire and Solothurn gained some independence. In 1038, Emperor Conrad II held court at Solothurn and there crowned his son, Henry III King of Burgundy. The royal court resided in Solothurn on several occasions until 1052, however, there is no evidence of a permanent royal palace. In 1127, it was acquired by the dukes of Zähringen. Under the rule of the Zähringens, in 1146, Solothurn's coins are first mentioned. In 1182, causidicus or Zähringen appointed judges first appeared in Solothurn. After the extinction of the Zähringer line in 1218 it became a free imperial city under the Holy Roman Emperor.

After the alliance with Bern in 1295, it became part of the Swiss Confederation. In 1382 the Habsburgs attacked the city, involving Solothurn in the Battle of Sempach. By the treaty of two years later, the Habsburgs renounced all claims to the territory of the city. The latter was expanded by acquisition of neighbouring lands in the 15th century, roughly coinciding with today's canton area. In 1481, it obtained full membership in the Swiss Confederation.

At the end of the Reformation, Solothurn maintained its Catholic religion. Between 1798 and 1803 the canton was part of the Helvetic Republic. In 1803 Solothurn was one of the 19 Swiss cantons that were reconstituted by Napoleon (Mediation). In 1830, the population rebelled against the aristocratic regime and the canton became definitely liberal-democratic. Even though the population was strictly Roman Catholic, Solothurn did not join the Catholic separatist movement (Sonderbund) in 1845-7. The territory of the canton now comprises land acquired by the former town, mainly in the Middle Ages. For that reason the shape of the canton is irregular and includes two exclaves along the French border, separated from the rest of the canton by Basel-Land, which form separate districts of the canton.

Swiss History Timeline - Solothurn (Soleure)
Solothurn coat-of-arms