The Battle of York was fought between the Vikings of the Great Heathen Army and the Kingdom of Northumbria on the 21 March 867. In the spring of 867 Ælla and Osberht put aside their differences and united in an attempt to push the invaders out of Northumbria. The battle started well for the Northumbrian forces, who were able to break through the city's defences. It was at this point that the experience of the Viking warriors was able to show through, as the narrow streets nullified any advantage of numbers the Northumbrians may have had. The battle ended with a slaughter of the Northumbrian army, and the death of both Ælla and Osberht.