[2] It was long ago theorized that the Brondings and Breca lived on the island of Brännö outside of modern Gothenburg (the second largest city in Sweden).
Karl P. Wentersdorf of Xavier University writes, "An adventure in which two youths spend seven days and nights swimming at sea is more than extraordinary, particularly since they are carrying heavy iron swords and wearing cumbersome coats of chain mail.
Unferth describes this as a foolhardy contest or race, but when Beowulf offers his own version of events, it becomes a youthful confidence-building or team-building shared challenge, much like a camping or mountaineering trip, in which the two participants endeavored to stay together rather than one leave the other far behind.
Although there are Nordic tales of swimming competitions, no other has characteristics of such extreme duration and danger as this – which, strictly speaking, was not a race but merely a testing of their own strength.
[16] Moreover, the duration of the challenge seems to make rowing more likely than swimming; seven days and nights immersed in Scandinavian waters, in winter no less (line 516), evidently without food nor an opportunity to go ashore for sleep or warmth, seems lethal (and certainly more arduous than Diana Nyad's five attempts – only the last one successful – to swim from Cuba to Miami, each effort lasting only 2½ days).
Second, it enables the introduction of a separate story (coming before the confrontation with Grendel) attesting, after a fashion, to Beowulf's strength, courage, and resourcefulness.
Further in the saga, when Heriot is being attacked by Grendel's Mother, we shall see Unferth approach Beowulf in humility, offering his own family's heirloom sword.