Solothurn (zōˈlōtŏrn) [key], Fr. Soleure, canton (1993 pop. 234,900), 306 sq mi (793 sq km), NW Switzerland. Very irregular in shape, Solothurn lies mostly in the Jura Mts. It is an important road and rail center. Cereals are grown and cattle are raised in the fertile valley of the Aare River. Manufactures include watches, jewelry, cellulose, paper, cement, auto parts, cotton textiles, shoes, iron and steel products, and electrical-communications equipment. The population is mainly German-speaking and Roman Catholic. Industry is largely concentrated in the towns of Olten and Solothurn (1993 pop. 15,600), the capital. Situated on the Aare, Solothurn was a Roman settlement called Salodurum. It had been a free town of the Holy Roman Empire since 1218 and was admitted to the Swiss Confederation in 1481. Until 1797, Solothurn was the residence of the French ambassadors to the Swiss diet and a center of cultural life. The town retains much of its historic character. It has old fortifications, a 13th-century clock tower, a 15th-century town hall, and the 18th-century Cathedral of St. Ursus and St. Victor, the see of the bishop of Basel and Lugano.