The Battle of Svolder (Svold, Swold) was a naval battle fought in September 999 or 1000 in the western Baltic Sea between King Olaf Tryggvason of Norway and an alliance of his enemies. The backdrop of the battle was the unification of Norway into a single state, long-standing Danish efforts to gain control of the country, and the spread of Christianity in Scandinavia. In later centuries, the saga descriptions of the battle, especially that in Snorri Sturluson's Heimskringla, have inspired a number of ballads and other works of literature.