A High Court fight has broken out over the location of "the first battle of 1066" with archaeologist Charles "Chas" Jones challenging a refusal by English Heritage to register Germany Beck at York as the site of the Battle of Fulford.
The "forgotten" battle is of historical significance because it was part of a real-life Game Of Thrones which culminated in the eventual defeat of Anglo-Saxon king Harold Godwinson by William of Normandy at the Battle of Hastings.
Mr Jones has carried out extensive research since 2000 and published "Finding Fulford - The search for the first battle of 1066."
He argues Germany Beck was the most probable site. It is also where Persimmon Homes has roused opposition by proposing to build 655 homes.
English Heritage, which protects and promotes historical sites round the country, took advice from a Battlefield Advisory Panel and refused in November 2012 to designate the Fulford site on an official Battlefield Register. The decision was upheld on review in July 2013.
English Heritage experts concluded that even though it was "probable" Germany Beck was the battlefield site the evidence was "insufficiently conclusive" to "securely identify" it for registration.
Ian Dove QC, for Mr Jones, argued at London's High Court that the decision cannot stand because the decision makers failed to apply the correct "location" test.
That involved consideration of whether there was evidence that a battle had occurred in a particular location "with a fair degree of probability".
The QC told Mr Justice Lindblom the test was contained in the Battlefield Designation Selection Guide: the only up-to-date statement of English Heritage's designation policy.
Mr Dove said it was uncontroversial that "absolute proof for the boundaries of a battle" was rarely possible.
Referring to English Heritage, he said: "If they did not apply the 'fair degree of probability' test to the question of location then unarguably they erred in law in the decision they reached."
Historians say the Battle of Fulford was the first of three battles which decided whether a Viking, Anglo-Saxon or Norman sat on the English throne and was a watershed in modern British history.
At the Fulford battle, a Viking army defeated an Anglo-Saxon force led by northern earls Edwin and Morcar.
The defeat forced Saxon king Harold, who was already facing a threat from William of Normandy, to march his army north and he defeated the Viking invaders at the Battle of Stamford Bridge five days later.
After his victory, Harold had to march his tired and battered army swiftly south again to take on William, who had launched his invasion.
Three weeks later Harold was defeated at the Battle of Hastings, resulting in 1066 being one history date generations of schoolchildren could remember.