The Battle of Assandun (or Essendune) was fought between Danish and English armies on 18 October 1016. There is disagreement whether Assandun may be Ashdon near Saffron Walden in north Essex or, as long supposed, Ashingdon near Rochford in southeast Essex, England.

It ended in victory for the Danes, led by Canute (Cnut)  the Great, who triumphed over the English army led by King Edmund Ironside. The battle was the conclusion to the Danish reconquest of England.

Following his defeat, Edmund was forced to sign a treaty with Canute. By this treaty, all of England except Wessex would be controlled by Canute and when one of the kings should die the other would take all of England, that king's son being the heir to the throne.

After Edmund's death on 30 November, Canute built a church, chapel or holy site after winning the battle to commemorate the soldiers who died in battle. A few years later in 1020 the completion took place of the memorial church known as Ashingdon Minster, on the hill next to the presumed site of the battle in Ashingdon.

The church still stands to this day. Canute attended the dedication of Ashingdon Minster with his bishops and appointed his personal priest, Stigand, to be priest there. The church is now dedicated to Saint Andrew but is believed previously to have been dedicated to Saint Michael, who was considered a military saint: churches dedicated to him are frequently located on a hill.