A tidal inland port on the Trent in Lindsey, where Sweyn Forkbeard based his conquest of England in 1013 and died on 3 February 1014.
Gainsborough stands on the east bank of the Trent in Lincolnshire, about eighteen miles north-west of Lincoln and more than fifty-five miles from the sea, yet it is a seaport in the sense that mattered in the eleventh century: the Trent is tidal this far up, and a fleet of shallow-draught ships could sail from the Humber into the heart of the Danelaw without portage.
That is why a Danish king chose it. In 1013 Sweyn Forkbeard brought his army here, took the submission of the north, and made Gainsborough the place from which he conquered England. He died here on 3 February 1014, and the fleet then chose his son Cnut as king in the same place.
The Trent at Gainsborough carries a tidal bore, the aegir, which runs upstream as a visible wave on the highest tides. It is a real and locally famous phenomenon, and it is the reason the river here behaves less like an inland waterway than like an arm of the sea.
The town’s name points to an older layer still. It derives from the Gaini, a folk of this stretch of the Trent, and the same people supply one of the few securely dated events in the town’s Anglo-Saxon history: in 868 Alfred the Great married Ealhswith, daughter of Æthelred Mucel, ealdorman of the Gaini — a marriage that tied Wessex to a Mercian family in this region a century and a half before the Danish fleets came.
Sweyn landed at Sandwich in the summer of 1013 and immediately sailed north to Gainsborough, which tells you his intention: this was not a raid for silver on the southern coast but a campaign run from a secure base among a population of Scandinavian descent. The magnates of Northumbria, Lindsey and the Five Boroughs submitted to him there, and he held his army back from plundering until it was south of Watling Street — a deliberate distinction between the Danelaw, which he was claiming as friendly, and the English south, which he was not.
By the end of 1013 Oxford, Winchester, Bath and finally London had accepted him, and Æthelred the Unready had fled to Normandy. Sweyn was king of England for a matter of weeks. He died suddenly at Gainsborough on 3 February 1014; the cause is not recorded. His body was taken back to Denmark, most probably to Roskilde, and the Danish fleet at Gainsborough chose Cnut in his place, while the English magnates recalled Æthelred.
This is recorded history rather than local legend. The Anglo-Saxon Chronicle names Gainsborough as Sweyn’s base and the place of his death, and the article previously described it as a place associated with him "in tradition", which understates what the sources actually say.
Gainsborough is sometimes offered as the setting for the most famous story told of Cnut: the king ordering the incoming sea to halt, in order to demonstrate to flattering courtiers that it would not. The Trent aegir makes the town an attractive candidate, since here is a tide that visibly advances on command of nothing.
The attribution does not survive examination. The story is first written down by Henry of Huntingdon, a century after Cnut, and Henry gives no location at all. Gainsborough’s claim rests on the suitability of its tidal bore, not on any source, and the tale itself may be a moral fable rather than a memory of anything Cnut did.
Domesday Book in 1086 records Gainsborough as a farming community of villeins and sokemen held by Geoffrey de Guerche — a manor of no special consequence, its brief period as the capital of a North Sea empire seventy years behind it.
Its surviving medieval monument belongs to the end of the Middle Ages. Sir Thomas Burgh acquired the manor in 1455 and built Gainsborough Old Hall between about 1460 and 1480: a timber-framed great hall with a brick tower and kitchens, and one of the best-preserved manor houses in Britain. Richard III was received there in 1483 and Henry VIII in 1541.