Viborg Bang

The war was essentially a border dispute between the Kingdom of Sweden, which at the time extended across the Baltic Sea to encompass what is now Finland and parts of Russia, and the Grand Duchy of Moscow.

Ivan calculated that Sten would be too preoccupied by the threat from Denmark-Norway to deal with a Muscovite incursion into Swedish Finland, and in late 1495 sent an army to seize the vital border castle at Viborg.

According to traditional Swedish accounts of the siege, Posse rigged one of the castle's gunpowder magazines to explode and then deliberately weakened the defences in that sector in order to encourage the Muscovites to attack.

When the besiegers duly stormed the weakened area of the walls, Posse detonated the magazine, causing a massive explosion which killed a large number of Muscovite soldiers and prompted the survivors to abandon the assault and lift the siege.

[5] There are no direct references in surviving source material to a massive explosion in connection with Viborg prior to 1539, when the Swedish polymath Olaus Magnus depicted it on his famous map the Carta Marina, and the actual term 'Viborg Bang' was not used until much later.