Little is known of Hastein's early life, described as a Dane in the Anglo-Saxon Chronicle, it is not for sure whether he was the son of Ragnar Lodbrok or was recruited by Ragnar to mentor his (other) son.  Between 834 and 835 he is recorded as participating in Viking raids on the island of Noirmoutier. He is credited with being involved with various raids on the Frankish Empire but is probably most famous for jointly leading a great raid into the Mediterranean in 859. 
For indeed the Frankish nation, which was crushed by the avenger Anstign [Hastein], was very full of filthy uncleanness. Treasonous and oath-breaking, they were deservedly condemned; unbelievers and faithless, they were justly punished... Dudo of St. Quentin's. Gesta Normannorum. Book 1. Chapter 3.
Spain and the Mediterranean
At first the raiding did not go well, with Hastein being defeated by the Asturians and later the Muslims of the Umayyad Caliphate of Córdoba at Niebla in 859. Success followed with the sacking of Algeciras, where the mosque was burned, and then the ravaging of Mazimma in the Idrisid Caliphate on the north coast of Africa, followed by further raids into the Umayyad Caliphate at Orihuela, the Balearic Islands and Roussillon.
Hastein and Bëorn wintered at Camargue island on the mouth of the Rhone before ravaging Narbonne, Nîmes and Arles, then as far north as Valence, before moving onto Italy. There they attacked the city of Luna. Believing it to be Rome, Hastein had his men carry him to the gate and tell the guards he was dying and wished to convert to Christianity. Once inside, he was taken to the town's church where he received the sacraments, before jumping from his stretcher and leading his men in a sack of the town. Another account has him wanting to convert before he dies and the following day feigns death. The city then lets 50 robed men come in for his burial all of which had swords under their robes. Hastein then jumps from his coffin and chops off the religious leaders heads on the way to sacking the city. As might be imagined, the veracity of this is much debated. He sailed down the coast and sacked Pisa and, sailing on the Arnoriver, Hastein ravaged Fiesole. The fleet then possibly raided Byzantine Empire sites in the eastern Mediterranean.
On the way back to the Loire, he stopped off in North Africa where he bought several African slaves (known to the Vikings as 'blámenn', blue men, possibly West Africans or Tuaregs) who he later sold in Ireland. Homeward bound, Hastein and Björn were defeated by a Muslim fleet soon after the Straits of Gibraltar, but still managed to ravage Pamplona before returning home to the Loire with 20 ships.
The Loire and the Seine
Settled back in Brittany, Hastein allied himself with Salomon, King of Brittany against the Franks in 866, and as part of a Viking-Breton army he killed Robert the Strong at the Battle of Brissarthe near Châteauneuf-sur-Sarthe. In 867 he went on to ravage Bourges and a year later attacked Orléans. Peace lasted until spring 872 when the Viking fleet sailed up the Maine and occupied Angers, which led to a siege by the Frankish king Charles the Bald and a peace being agreed in October 873.
Hastein remained in the Loire country until 882, when he was finally expelled by the Charles and then relocated his army north to the Seine. There he stayed until the Franks besieged Paris and his territory in the Picardy was threatened. It was at this point he became one of many experienced Vikings to look to England for riches and plunder.
Hastein's Army in England
Hastein first crossed to England from Boulogne in 892 leading one of two great companies. His army, the smaller of the two, landed in 80 ships and occupied the royal village of Milton in Kent, whilst his allies landed at Appledore with 250 ships. Alfred the Great positioned the West Saxon army between them to keep them from uniting, the result of which was that Hastein agreed terms, including allowing his two sons to be baptised, and left Kent for Essex. The larger army attempted to reunite with Hastein after raiding Hampshire and Berkshire in the late spring of 893, but was defeated at Farnham by an army under Prince Edward, Alfred's son. The survivors eventually reached Hastein's army at Mersea Island, after a combined West Saxon and Mercian army failed to dislodge them from their fortress at Thorney.
As a result, Hastein combined his forces from Appledore and Milton and withdrew them to a fortified camp at Benfleet, Essex. He used this camp as a base to raid Mercia. However, while his main force was out raiding those left in the fort were defeated by the bolstered militia of eastern Wessex. The West Saxons captured the fort, along with the ships, booty, women and children. This included Hastein's own wife and sons. Hastein re-established his combined force at a new fort at Shoebury further north in Essex, and received reinforcements from the settled Danes of East Anglia and York. Shortly after, according to the Anglo-Saxon Chronicle, Hastein held talks with Alfred, possibly to discuss terms for the release of his family. Whatever the discussion, it seems Hastein had his two sons returned to him. The Anglo-Saxon Chronicle tells us that it was because Alfred and Alfred's son-in-law Aethelred of Mercia, had stood sponsor to Hastein's sons at their baptism in early 893, before Hastein had arrived at Benfleet. Thus Alfred was godfather to one boy and Aethelred godfather to the other
If Alfred's strategy was to create peace then it was a failure as shortly after, Hastein launched a second raid along the Thames valley and from there along the River Severn. Hastein was pursued all the way by Aethelred and a combined Mercian and West Saxon army, reinforced by a contingent of warriors from the Welsh kingdoms. Eventually the Viking army was trapped at Buttington, this was possibly the island of Buttington on the Severn near Welshpool, Powys, then at the resulting Battle of Buttington several weeks later they fought their way out , and lost many men, and returned to the fortress at Shoebury. According to the annals:
..after many weeks had passed, some of the heathen [Vikings] died of hunger, but some, having by then eaten their horses, broke out of the fortress, and joined battle with those who were on the east bank of the river. But, when many thousands of pagans had been slain, and all the others had been put to flight, the Christians [English] were masters of the place of death. In that battle the most noble Ordheah and many of the king's thegns were killed... 
In late summer 893, Hastein's men struck out again. They moved all their booty, women and ships, from East Anglia, to a ruined Roman fortress at Chester. The plan was to rebuild the fortifications and use it as a base for raiding northern Mercia. However, the Mercians had other ideas, they laid siege to the fortress and attempted to starve the Danes out by removing or retrieving any livestock and destroying any crops in the area.
In the autumn the besieged army left Chester, marched down to the south of Wales and devastated the Welsh kingdoms of Brycheiniog, Gwent and Glywysing until the summer of 894. They return via Northumbria, the Danish held midlands of the Five Burghs, and East Anglia to return to the fort at Mersea Island. In the autumn of 894, the army towed their ships up the Thames to a new fort on the River Lea. In the summer of 895 Alfred arrived with the West Saxon army, and obstructed the course of the Lea with a fort either side of the river. The Danes abandoned their camp, returned their woman to East Anglia and made another great march across the Midlands to a site on the Severn (where Bridgnorth now stands), followed all the way by hostile forces. There they stayed until the spring of 896 when the army finally dispersed into East Anglia, Northumbria and according to the Anglo-Saxon Chronicle, those that were penniless found themselves ships and went south across the sea to the Seine.
Hastein disappeared from history in around 896, by then an old man having already been described as "the lusty and terrifying old warrior of the Loire and the Somme", when he arrived in England several years earlier. He was one of the most notorious and successful Vikings of all time, having raided dozens of cities across many kingdoms in Europe and North Africa.
The Norman monk Dudo of St. Quentin was very critical of Hastein:
This was a man accursed: fierce, mightily cruel, and savage, pestilent, hostile, sombre, truculent, given to outrage, pestilent and untrustworthy, fickle and lawless. Death-dealing, uncouth, fertile in ruses, warmonger general, traitor, fomenter of evil, and double-dyeded dissimulator...Dudo of St. Quentin's. Gesta Normannorum. Book 1. Chapter 3.
Jarl Hastein is a recurring character in Bernard Cornwell's The Saxon Stories, as a former ally and then opponent of Uhtred of Bebbanburg. Jarl Hastein also appears in the fictional series The Strongbow Saga written by Judson Roberts. The Old Gods expansion pack for 2012's Crusader Kings II makes it possible to play as Hastein.
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