In late May or early June he moved his forces eastward and met Cnut’s army at Pensellwood, near Gillingham in Dorset in a battle whose outcome is described by chroniclers as indecisive. Moving on, the two forces met again at Sherston near Malmesbury, in a battle lasting two day and where “there was great slaughter on both sides”. Edmund’s force was gaining the upper hand until the traitor Earl Eadric arrived with fresh troops from the midlands to aid Cnut.
Edmund’s determination kept the balance of the fighting in his favour until Eadric cut off the head of one Osmear whose face and hair were much like Edmunds. In the words of Florence of Worcester, he shouted “oh ye Wessex men! Flee quickly, you have lost your leader”. Edmund’s troops were panicked, but rallied and continued the fight until dark when Cnut’s forces slipped away and headed back towards London. The battle is remembered locally in the legend of John Rattlebone, a local hero killed in the fight. The Sherston Rattlebone Inn is named in his memory.
Edmund also returned to the capital, having raised more shire levies and marched east, keeping to the north side of the Thames. He caught the Danes off guard and managed to break through their lines and relieve the garrison, driving the Danes back to their ships. A few days later Edward forded the river at Brentford and attacked the Danes encamped on the south bank where they are said to have “fought the host and put it to flight”.
The English however suffered a number of unnecessary casualties when some of the army, having gone ahead in search of plunder, somehow drowned in the river. Edward was again forced to retreat and returned to Wessex to raise a fresh army. The Danes returned to their entrenchments and, according to the Chronicle, “attacked London fiercely by land and water”, but after such a long siege, they were running out of supplies and Cnut was forced to withdraw his ships to his base in the Orwell estuary. Edmund knew that to defeat the Danes once and for all he would need more troops and “called up all the people of England”. Cnut sailed to the Medway to refit his fleet before beginning another assault, ordering the bulk of his force to march overland to join him. Edmund led his new army across the Thames in pursuit and met with the Danes at Otford. In the ensuing fight, the Danes were broken and fled to Sheppey, pursued by Edmund who “slew as many as he could overtake.”
His victory would have been even more complete if he had not agreed to meet with the cunning Eadric at Aylesford who, realising that Edmund was winning, asked for pardon and promised loyalty to him. Surprisingly Edmund accepted Eadric’s word. The Chronicle reports that “no greater error of judgement was ever made than this”. Cnut learned of his movements and marched after him and on October 18th 1016AD, surprised Edmund’s more numerous forces at Assandun or Ashdon in Essex.
The two sides met on level ground between their two camps according to the Encomium Emmae, at the hour after Matins, that is nine o’ clock in the morning. It goes on to relate the legend of Cnut’s war banner, normally of plain white silk, but on which, a black raven mysteriously appeared when victory grew imminent, snapping its beak and flapping its wings. The battle was fiercely fought and went on till darkness, a not uncommon practise in such evenly matched battles when, even if losing, it was better to stand and fight to the last rather than turn your back to the enemy when you would certainly be pursued and killed.
Edmund again showed superior tactics and was gaining the advantage when Eadric, treacherous to the last, withdrew his forces leaving Edmund’s flank open to the enemy. Cnut’s army rallied and threw the English into confusion, killing many with the remainder managing to slip away in the darkness. Whether it was by prior arrangement or simply cowardice that made Eadric withdraw is not known, but given his track record, the former seems likely. The Chronicle says of Eadric,”he did as he had so often before: he and his forces were the first to set the example of flight and thus betrayed his royal lord and the nation”.
Edmund was forced to sign a treaty with Cnut, known as the The Compact of Olney, in which he was given control of Wessex with Cnut ruling the rest of the country. In addition, Edmund agreed to levy a Danegeld tax to support Cnut’s army. It is said that the two met on a small island on the Severn near Deerhurst, having crossed from opposite banks by rowing boat. The treaty also stated that, should either die, the other would inherit the entire kingdom. This might have seemed a good deal for Edmund but on the 30th of November he died, probably from wounds received at Ashton, although there are many other versions of his death.
From now on, England was to have a Danish king. It would be many years before the English line was restored.