The exact year of the battle is unknown, but is generally considered to have taken place between 870 and 900. This uncertainty is due to lack of sources, and partly because the Christian calendar was not introduced at the time. The sagas follow the convention of counting the number of winters passed since an event. A traditional date of the event, the year 872, is a 19th-century estimate. In the 1830s, the historian
Rudolf Keyser counted the number of years backwards from the
Battle of Svolder as recorded in
Snorri Sturluson's
Heimskringla, dating the battle to 872. Keyser's chronology was popularized by the works of the historian
P. A. Munch, and by that time still unchallenged, this year was chosen for the millennial celebration of the unification of the Norwegian state in 1872. In the 1920s, using similar methods as Keyser but highly critical to the reliability of the sagas, the historian
Halvdan Koht dated the battle to about 900. For the next fifty years, this chronology was regarded by most scholars as being most likely. In the 1970s, the Icelandic historian
Ólafia Einarsdóttir concluded that the battle took place somewhere between 870 and 875. However still disputed, most scholars will agree that the battle took place during the 880s. ==Memorials==