King of Denmark (1146–1157) in the war of the three kings, whose treacherous attack at the Bloodfeast of Roskilde and defeat and death at Grathe Heath ended the civil wars and raised Valdemar I.
Sweyn III, called Sweyn Grathe, was one of the three rival kings of Denmark during the civil war of 1146–1157. Son of the fierce Eric Emune, he was elected king in Scania and Zealand after Eric Lamb's abdication, while Canute V was raised up in Jutland — beginning a decade of war for the crown into which the young Valdemar was also drawn.
After years of fighting, the three agreed to partition Denmark at a reconciliation feast at Roskilde in 1157. There Sweyn treacherously attacked his rivals — the "Bloodfeast of Roskilde" — killing Canute V and wounding Valdemar, who escaped. Valdemar raised Jutland against him and destroyed Sweyn's army at Grathe Heath later that year; Sweyn was killed in the rout, leaving Valdemar sole king and founder of a new age.
Sweyn was born about 1125, the son of King Eric II Emune. When Eric Lamb abdicated in 1146, the kingdom's deep divisions surfaced at once: the assemblies of the different provinces chose different kings. Sweyn was elected in Scania and Zealand, while in Jutland the magnates raised up Canute V, grandson of King Niels.
Neither would yield, and the young Valdemar — son of the murdered Canute Lavard — held the balance between them, allying now with one, now the other.
Sweyn Grathe is remembered as an able but arrogant and untrustworthy king, whose reign is defined by the treachery that destroyed it. The sources, largely favourable to his ultimate conqueror Valdemar, present him as capable and cultivated — he brought German customs and courtly manners to Denmark — but also proud, grasping, and faithless.
It is the Bloodfeast of Roskilde that fixed his reputation. Having sworn peace and partition with his rivals, he broke the oath in the most sacred setting of hospitality, turning a feast of reconciliation into a massacre. Whether from ruthless ambition or desperation, the act branded him a treacherous king, and his swift destruction at Grathe Heath was read by his enemies as the just punishment of a broken faith.
For a decade Denmark was torn between Sweyn, Canute V, and Valdemar, in shifting alliances and open war. Exhausted, the three at last agreed in 1157 to divide the kingdom between them, sealing the settlement at a great feast in Roskilde.
At that feast Sweyn sprang his trap. His men fell on his fellow kings: Canute V was killed outright, but Valdemar, though wounded, cut his way out and fled to his native Jutland. The Bloodfeast of Roskilde turned the whole country against Sweyn.
Valdemar raised Jutland in arms, and the two surviving kings met in battle on Grathe Heath, in central Jutland, on 23 October 1157. Sweyn's army was routed. Sweyn himself, fleeing the field, was caught and killed by peasants. His death ended the war of the three kings and left Valdemar sole ruler of Denmark.
Sweyn Grathe is remembered as the treacherous loser of the war of the three kings, the king whose broken oath at Roskilde and defeat at Grathe Heath cleared the way for Valdemar I. His fall marks the end of the long Danish civil wars and the dynastic strife that had begun with the murder of Canute Lavard, and the beginning of the Valdemar era in which Denmark rose to new power.