The Great Heathen Army was much larger and aimed to conquer and occupy the four kingdoms of East Anglia, Northumbria, Mercia and Wessex.

The force was led by three of the five sons of the semi-legendary Ragnar Lodbrok, including Halfdan Ragnarsson, Ivar the Boneless and Ubba.

The invaders initially landed in East Anglia, where King Edmund provided them with horses for their campaign in return for peace.

The Anglo-Saxon Chronicle does not mention the reason for this invasion, perhaps because Viking raids were fairly common during that period of time.

[14] The first monastery to be raided was in 793 at Lindisfarne, off the northeast coast; the Anglo-Saxon Chronicle described the Vikings as "heathen men".

[16] The Anglo-Saxon Chronicle for the year 840 says that Æthelwulf of Wessex was defeated at Carhampton, Somerset, after 35 Viking ships had landed in the area.

[28][29] Sawyer notes that the Anglo-Saxon Chronicle of 865 referred to the Viking force as a Heathen Army, or in Old English "hæþen here".

The historian Richard Abels suggested that this was to differentiate between the Viking war bands and those of military forces organised by the state or the crown.

[32][33] Guy Halsall reported that, in the 1990s, several historians suggested that the Great Heathen Army would have numbered in the low thousands and acknowledged that there "is still much room for debate".

[34] By the time the war had ended, the Vikings had discovered that monasteries and towns situated on navigable rivers were vulnerable to attack.

[27] Several of the Viking leaders who had been active in Francia and Frisia joined forces to conquer the four kingdoms constituting Anglo-Saxon England.

The Anglo-Saxon historian Æthelweard was very specific in his chronicle and said that "the fleets of the viking tyrant Ivar the Boneless landed in England from the north".

[34][35] The Vikings had been defeated by the West Saxon King Æthelwulf in 851, so rather than land in Wessex they decided to go further north to East Anglia.

[20][34][36] Legend has it that the united army was led by the three sons[c] of Ragnar Lodbrok: Halfdan Ragnarsson, Ivar the Boneless (Hingwar), and Ubba.

[20][34][36] Norse sagas consider the invasion by the three brothers[d] as a response to the death of their father at the hands of Ælla of Northumbria in 865, but the historicity of this claim is uncertain.

[37][8] In late 865, the Great Heathen Army encamped in the Isle of Thanet and was promised by the people of Kent danegeld in exchange for peace.

In 867, the Northumbrians paid danegeld, and the Viking Army established a puppet leader in Northumbria before setting off for the Kingdom of Mercia, where in 867 they captured Nottingham.

A combined army from Wessex and Mercia besieged the city of Nottingham with no clear result, so the Mercians settled on paying the Vikings off.

[41] The reinforced Viking army turned its attention to Wessex but the West Saxons, led by King Æthelred's brother Alfred, defeated them on 8 January 871 at the Battle of Ashdown, slaying Bagsecg in the process.

[45] In 874, following their winter stay in Repton, the Great Heathen Army drove the Mercian king into exile and finally conquered Mercia.

This was followed closely by what was described by Asser as the Treaty of Wedmore, where Guthrum agreed to be baptised and then for him and his army to leave Wessex.

Evidence for this is the presence of two Viking cemeteries in Derbyshire that are believed to be connected to the Great Army, at Repton and at Heath Wood.

It seems they were partly discouraged by the defeat of Guthrum but also Alfred's success against the Vikings coincided with a period of renewed weakness in Francia.

The Frankish emperor, Charles the Bald, died in 877 and his son shortly after, precipitating a period of political instability of which the Vikings were quick to take advantage.

Due in part to the King's efforts to resist the invaders and defend Wessex, the Heathen Army made less of an impact against the kingdom than hoped and saw little progress, eventually disbanding in 896.

[62][63] Every freeman in the land could be called out to protect the realm in times of trouble but the speed of Viking hit-and-run raids had been too quick for the local militias to act; part of Alfred's reforms was to create a standing army that could react rapidly to attacks.

[64] To maintain the burhs, as well as the standing army, Alfred set up a system of taxation and conscription that is recorded in a document now known as the Burghal Hidage.

[65] The burhs were connected with a network of military roads, known as herepaths, enabling Alfred's troops to move swiftly to engage the enemy.

[66] A common Viking tactic was to seize a centre, usually some sort of fortification, that they could reinforce and then use as a base to plunder the surrounding district.

[66] By 896, the Viking army was all but defeated and no longer saw any reason to continue their attacks and dispersed to East Anglia and Northumbria.