The sword I was thinking of discussing was the one that he found in Grendel's cave, the one that is the work of giants, the 'ealdsweord eotenisc'(1558) 'giganta geweorc'(1562). Whether eoten are Jutes or giants is still debated but the consensus is that they are giants. There is no doubt about the meaning of 'giganta'. Unferth's sword does not even scratch Grendel's mother so Beowulf threw it down and prepared to fight bare-handed and die when he saw this amazing sword. It was able to pierce her magically protected hide but it melted away from the poisonous heat of her blood.
Of course in a story with sea-monsters, a dragon, Grendel and his mother and Weland, too, why should there not also be giants? In two Anglo Saxon poems, The Ruin and The Wanderer, we have the phrase again - 'work of giants'. In The Ruin (in fragments), it refers possibly to the ruins of Bath as the poet comes upon them and wonders about the builders in stone and the fate that took them. He refers to the city as 'enta geweorc' as are the ruins in The Wanderer. The Anglo Saxons did not build in stone so Roman ruins were a marvel to them and the deserted cities were the habitations of ghosts and demons. So, my thought is that, if Beowulf found a strange old sword, that was the work of giants, was it a Roman sword that he held in his hand? After all there were many heated battles between the Romans and the Germanic tribes. The Teutoburger Wald where Augustus lost three legions, one quarter of the entire Roman army, to a Cheruscan leader, Arminius, is one such place. The sites of the Batavian uprising are another. It would be an intriguing thought, since the Teutoburger Wald was a boggy place, that maybe Grendel's mere was located there but it really is too far from Leire, the site of Hrothgar's court. Anyway, Roman swords built tough to last just like their walls.