On this day, the 9th (maybe, the history isn't that clear) of September 1000, the largest battle of the Viking Age took place. A vast fight between the Norwegian King Olaf and an alliance of the Kings of Sweden and Denmark, and the Norwegian enemies of Olaf.
The battle was organised as a result of the unification of Norway by Olaf, and the subsequent efforts of Christian conversion. Denmark wished to seize control of Norway, and Olaf's efforts had halted that.
There are many accounts of the battle, but the most detailed come from sources written hundreds of years later, the King's Sagas. Fairly unreliable, but they give novel insight into the preceding events of the battle, a problematic marriage for Olaf.
Unsurprisingly marriage is often a source of contention when it comes to royalty.
A gruesome affair, King Olaf was ambushed whilst returning home from a campaign. 11 Norwegian warships faced against more than a conglomerated 70, resulting in a predictable catastrophic loss for King Olaf.
Reportedly, however, both sides faced heavy losses. The battle climatically ended with Olaf taking his own life, thrusting himself from his ship and into the sea. Better for him to kill himself than see defeat at the hands of his enemies.
Norway was subsequently split between the Danes and Swedes, undoing much of Olaf's unification. However his legacy still remains in the form of the spread Christianity to the north.