What this song renders
The route in the verses is the Chronicle’s. In 1013 Sweyn came to Sandwich, then sailed round to the Humber and up the Trent to Gainsborough, where Earl Uhtred and the Northumbrians, the people of Lindsey and the Five Boroughs, and everyone north of Watling Street submitted and gave hostages. Once he crossed the Street going south, the Chronicle says, his army did the worst damage any army could. Oxford and Winchester submitted, London resisted, and he went west to Bath, where the western thegns submitted too. London then gave in for fear of him.
Æthelred sent Emma over the sea to her brother Richard in Normandy that year, with their sons sent after her, and followed himself around the new year. Sweyn was accepted as “full king” by the end of 1013 and died at Gainsborough on 3 February 1014. The bridge’s choice to leave, and her reasoning — I learned it at Saint Brice — are the song’s own.
The motive the chorus gives him, he comes for his sister, is a legend. William of Malmesbury, writing more than a century later, says that Sweyn’s sister Gunhild was among the victims of St Brice’s Day and that his invasions were revenge. No contemporary source says so. Eleven years he kept the count is also compression: Sweyn raided in person in 1003 and 1004, and the great Danish armies of 1006–07 and 1009–12 are not recorded as his.
The 1013 campaign, from Sandwich and Gainsborough to the submissions of Oxford, Winchester, Bath and London, is documented in the Anglo-Saxon Chronicle, as are Emma’s flight to Normandy, Sweyn’s acceptance as king and his death in February 1014. That he came to avenge a sister killed on St Brice’s Day is a twelfth-century legend. The eleven years of counting and Emma’s reasons for leaving are the song’s staging.