Glamdring was the magical and powerful sword of the Noldo King Turgon. Glamdring was arguably the best blade recorded being discovered in the Third Age. Glamdring was hated by the Goblins more than the sword Orcrist. Glamdring glowed Blue when orcs were near, but it also had the ability to turn into a holy white when facing dark servants of Morgoth (like the Balrog of Moria). Eventually the sword was found by Gandalf and Thorin's company after the death of William, Tom and Bert Huggins. How exactly the three mystical items of Gondolin came to be in an area of the Ettenmoors, was a mystery. The making of the blade was also a mystery, but it is was most likely a work of either Maeglin Lómion or Enerdhil, the two greatest Smiths of Gondolin at the time of it's fall.
Glamdring was so mighty that the blade could kill an orc, troll, or Great Goblin with one strike--it could block and shatter the blade of a Balrog, and the mention of the blade struck fear into all orcs.
Speculation[]
It can be hypothesized from Elrond Half-elven's words, that the three trolls plundered other plunderers. A generalized consensus on how Glamdring appeared beyond the borders of Beleriand can be seen here: After the fall of Gondolin, Celebrimbor took the artifacts of Gondolin with him after the War of Wrath. Celebrimbor then took the heirlooms to Ost-in-edhil in the Second Age. After the destruction of Ost-in-edhil in the Second Age, the armies of Sauron confiscated the weapons. The forefathers of the three trolls then attained the artifacts by taking them from others. Eventually the three trolls got them passed to them during the Third Age after they came to adulthood.