According to legend, the Great Heathen Army was assembled by the sons of Ragnar Lodbrok to avenge the death of their father at the hands of King Aella of Northumbria. While this cannot be confirmed, a Viking army, larger than any previous invading forces, descended on England in 865 CE. Over more than a decade, they conquered large swaths of England, forcing the Anglo-Saxons to come to terms, leading to the establishment of large regions of Danelaw across the country. How big was this army, where did they come from, and how did they conquer so much of England?Where Did the Great Heathen Army Come From?Gravestone marker from Lindisfarne showing men attacking with Viking-style swords, c. 900. Source: Wikimedia CommonsThe name Great Heathen Army comes from the Anglo-Saxon Chronicle, but that text gives no reason for the arrival of a larger-than-normal Viking army in England in 865 CE.The Vikings had been raiding England from the end of the 8th century, traditionally starting with the raid on the monastery at Lindisfarne in 792 CE. These were smash-and-grab operations with Viking warriors arriving in their agile ships to attack unfortified communities and undefended monasteries. Defenses were seen as unnecessary since no Christian would dream of desecrating a monastery, but as the English noted, these piratical raiders were heathens. The Vikings took whatever was of value including sacred gold and silver objects, and people to sell as slaves to their networks in the east. The arrival of the Great Heathen Army marked a change in approach. This army did not intend to take what it wanted and leave, but rather to conquer.The Norse Saga of Ragnars Sons suggests a reason for the large-scale attack. The legendary Viking Ragnar Lodbrok, a king of Denmark and Sweden, was raiding Northumbria when he was defeated and captured by King Aella of Northumbria, who killed him by throwing him in a snake pit. His sons wanted revenge, and three of his sonsHalfdan Ragnarsson, Ivar the Boneless, and Ubbaare specifically named among the leaders of the great army.A manuscript depiction of Danes landing from ships, from MS M.736 fol. 9v, 12th century. Source: The Morgan Library, New YorkThis scenario, which only appears in the Norse sources and not in any of the Anglo-Saxon sources, is difficult to verify because Ragnar is a semi-legendary figure. While there was probably once a powerful Viking leader called Ragnar Lodbrok, it is unclear when he lived and which of the many escapades attributed to him belonged to the historical figure. This explanation may have fit better within the Norse tradition of heroic storytelling than the historical facts when the story of Ragnar and his family was written down in the 13th century.Historians note that in the decades preceding the great invasion of England, Viking mercenaries were active in Francia, participating in the conflict between Emperor Louis the Pious and his sons. While there, the Vikings discovered that in addition to coastal targets, monasteries and settlements on navigable rivers were vulnerable to attack. This led to the Viking attack on Paris in 845, which saw the raiders bought off with a large payment of silver. Smaller-scale attacks continued, but the Franks were also busy fortifying towns and rivers, limiting profitability.This mercenary force may have been looking for new profitable ventures, and England may have looked like a place where the strategies that had previously served them well in Francia might work. A mercenary force could explain why the Great Heathen Army seems to have been composed of people from throughout the Viking world, including Denmark, Sweden, and even Ireland. The raiding force may also have come from more than one place. According to the Anglo-Saxon historian Aetheleard, a fleet led by Ivar the Boneless landed in the north, while the Anglo-Saxon Chronicle says they landed at Thetford in East Anglia.Landing and Initial Progress of the Great Heathen ArmyMap of the movements of the Great Heathen Army. Source: Wikimedia CommonsThe Great Heathen Army reportedly landed at Thetford in East Anglia in 865 CE. The East Anglian King Edmund immediately tried to buy the Vikings off, providing them with horses in exchange for peace. The Viking army seems to have wintered there without major incident.When the campaign season started in 866, the army made its way north to York. This may have been to join with separate forces led by Ivar the Boneless. According to the Norse sagas, while his brothers rushed into battle, Ivar instead established a kingdom for himself based around York in the south of Northumbria, making alliances with the locals. Passing directly through Mercia to York could be explained by the need to meet up with Ivar and his army and fortify this stronghold, rather than a particular grudge against King Aella of Northumbria.Scene on the Stora Hammar Stone that may show a blood eagle execution, Gotland, Sweden, c. 7th century. Source: Wikimedia CommonsIn the following years, the army raided south into Mercia and ravaged Northumbria in the north. At least part of the army is known to have wintered in Nottingham in 867 as a stronghold in Mercia and made peace terms with the Mercians in the same year. In 867, King Aella was killed, reportedly using a method known as the Blood Eagle to punish him for his crimes. Ragnars son Bjorn Ironside may have been present. In 869, they returned to East Anglia and their base at Thetford. They killed King Edmund and took control of the territory.Activity intensified in 871 when reinforcement arrived from Scandinavia in the form of the Great Summer Army. This enlarged force enabled the Vikings to turn their attention to Englands strongest kingdom, Wessex. They were not initially successful and were defeated by the West Saxon forces at the Battle of Ashdown in 871. However, the people of Wessex believed that the threat was great. When Alfredlater known as Alfred the Greatcame to power in Wessex about three months after this battle, he bought peace from the Vikings. The Vikings wintered in London, on the edge of Wessex territory, in 871/872.How Big Was the Great Heathen Army?Viking artifacts recovered from Torksey, c. 9th century. Source: Archaeology.orgFollowing peace negotiations with Wessex, in the campaign season of 872, the Vikings decided to focus on Mercia. After the forces in London returned to York to gather reinforcements, they established a new camp for themselves at Torksey in Mercia.This camp is interesting because it has been examined by archaeologists based on the plotting of archaeological finds discovered by metal detectors. Over the years they have found ingots, weights, 9th-century coins, and more than 120 Arabic silver dirhams. This is a strong indicator of a Viking presence, as they acquired these Dirhams through trade in the East.When all the finds are plotted, it suggests that the Viking camp covered an area of around six acres. It was also a fortified position, as in the 9th century, their camp would have been on an island enclosed by the River Trent on one side and marshlands on the other three sides. A camp of this size could have accommodated several thousand people.Similar Viking artifacts found at a Viking camp at Aldwark, North Yorkshire, c. 9th century. Source: National University of IrelandBefore the discovery of this site, estimates for the size of the Great Heathen Army were between 1,000 and 3,000 men. This site suggests that the army, at least by 872, was probably much larger. This was also not the full army, as there were still Vikings holding York.The nature of the artifacts found also suggests that the camp did not just hold warriors. There is evidence of trade, and the presence of spinning whorls and other tools to make textiles suggest that women were present in a non-military capacity. These findings also reinforce the idea that this Great Heathen Army arrived with a different purpose than the previous small raiding parties. They intended to take land to settle their families.In 873, this band of warriors subdued Mercia, forcing its king to flee and placing a puppet king in his place.Viking Burials at ReptonExcavated grave of a Viking warrior found at Repton, c. 9th century. Source: Martin Biddle via Archaeology MagazineThe battle for Mercia seems to have been a bloody one, as indicated by excavations at Repton. The Vikings seem to have camped there in the winter of 873-874, from where they raided despite promises made to Mercia.Excavations show that the Vikings fortified their camp at Repton, creating a D-shaped enclosure near St Wystans Church. This was supported by a defensive ditch that was dug straight through a Mercian cemetery to meet the River Trent. They seem to have had no problem destroying what was already there, as the remains of at least ten carved Anglo-Saxon stone crosses have been found in the earthworks.There were bloody battles between the Vikings and the Mercians. The body of a man who must have been a Viking chief was found near the tombs of the Mercian royal family. He was buried with an iron sword and a silver Thors Hammer amulet around his neck. This does not seem to have offered him much protection, as his death was bloody. There is evidence that he was stabbed in the eye, that his body was hacked at from above with a sword or an axe, and a boar tusk between his thighs may indicate that his genitalia was damaged.Thors Hammer Mjolnir pendant found at Repton, c. 9th century. Source: University of NottinghamAnother 264 bodies, around 80% of which belonged to adult males, were found in a channel mound just outside the fortified enclosure. Radiocarbon dating and coins from 872-874 suggest that they also belong to this period of Viking encampment. Many of the bodies show signs of trauma and violent deaths. Their bodies seem to have been transported from elsewhere to be buried, verifying that the Vikings were in the habit of collecting their dead from the battlefield for proper internment.Among the varied archaeological remains are several clinker nails used in the construction of Viking ships. This suggests that the Vikings had ships with them, taking advantage of rivers and sometimes carrying their ships overland when necessary.War With Wessex and DanelawIllustration of the Vikings attacking a town, Pierpont Morgan Library MS M.736, folio 10r, c. 12th century. Source: Morgan Library and MuseumAfter the conquest of Mercia, the Vikings were in control of East Anglia, Mercia, and Northumbria. At this point, the Viking army split in two. One group, possibly led by Halfdan Ragnarsson, stayed in Northumbria. They reportedly raided into Scotland, crossing the River Tyne and battling with the Picts in 875. By 876, they were settling in Northumbria with their families, plowing the land.The second band, led by a man called Guthrum, who arrived from Denmark with the Great Southern Army, headed south for renewed conflict with Wessex. They were in Cambridge in 874 and Wareham in 875. They made a treaty with Alfred the Great that year but continued to raid and were paid off repeatedly.This resulted in the Battle of Edington in 878 when the troops of Wessex finally defeated the Vikings, whom they had previously been unable to dislodge from their defensive positions. The Vikings took refuge in Chippenham, which was well fortified, but the West Saxons starved them out. After two weeks, they sued for peace. While this was far from the first peace treaty between the Vikings and Wessex, Alfred was more confident that this would hold due to his decisive victory at Edington and the fact that Guthrum agreed to be baptized.Map of Danelaw division. Source: Wikimedia CommonsNot long after, a further treaty was struck known as the Treaty of Alfred and Guthrum. It created a boundary between Anglo-Saxon land and Viking land. South of the line, Anglo-Saxon law was to apply, north of the line was to be governed by the Vikings under what would become known as Danelaw. The treaty also agreed on a wergild price to be paid when Englishmen or Danes were slain in acts that broke the peace. This treaty would remain in place for around 50 years.The End of the Great Heathen ArmyThe Viking leader, Guthrum, surrendered to Alfred the Great and agreed to be baptized, by James William Edmund Doyle, 1864. Source: Wikimedia CommonsFollowing his agreement with Alfred, Guthrum withdrew from Wessex and remained in East Anglia and Mercia, with the other part of the Great Heathen Army still in Northumbria based around York. Many Vikings settled and became relatively integrated with the local population. Others seem to have gone to Francia following the treaty to take advantage of the opportunities presented by new conflicts there.In 892, after the death of Guthrum, there was an attempt to renew hostilities. There are reports of a fleet of 250 Viking ships at Appledore in Kent and another 80 at Milton Regis. While these forces attacked Wessex territory, they were not able to have the same impact.Alfred had learned from the years of conflict and had constructed a navy, reportedly with ships around twice as long as Viking vessels, blocking their access to many waterways. He also established a system of fortified towns known as burghs and a standing army that could respond quickly to any threat. Around 20 percent of the male population may have been conscripted, creating a significant force of around 27,000 men. With little success, this new Viking army was disbanded in 896.Conflict between the Vikings and the Anglo-Saxons would continue. For example, the Vikings were expelled from York in 954, but then Sven Forkbeard and Cnut the Great would become kings of all England in the early 11th century. This back and forth, which started with the arrival of the Great Heathen Army, would only end with the Norman Conquest of England in 1066.