Viborg (mod. Vyborg, Russia) was a Swedish fortress, founded in 1293 during the so-called Third Swedish Crusade against Karelia.
The fortress was located on an island in the western estuary of the river Vuoksi that linked Lake Ladoga and the Gulf of Finland. An attempt to gain control over the eastern estuary into Lake Ladoga at Kexholm a year later failed. A further attempt in 1300 to control the Neva link between Lake Ladoga and the Baltic Sea by founding the fortress of Landskrona likewise failed, and so Viborg remained the cornerstone in Sweden’s defense against Russia and in future crusades toward the east. On numerous occasions Novgorod and later Moscow tried to take Viborg, always in vain. The Russians came closest to achieving this during the war in 1495-1497, which was also the last occasion when a Swedish ruler obtained a crusading bull from the pope against the Russians.