City, port, and capital of Sor-Trondelag county, on the Trondheimsfjord, 250 mi N of Oslo, central Norway. Founded by Olaf I Trygvesson of Norway in a.d. 997, it was the political and religious capital of medieval Norway but declined after the forced introduction of the Reformation in 1537. It regained economic importance in the 19th century. Haakon VII was crowned as the first king of an independent Norway in Trondheim Cathedral in 1906. It fell to Germany in World War II on April 9, 1940, and became an important German naval base, frequently bombed by the Allies. It was the center of the Norwegian resistance.