Borlin inspired a large number of dwarven warriors to form the Mithril Legion and embark on a quest to reclaim the Mines of Tethyamar. They marched out of Tilverton in the Year of the Wave, 1364 DR, heading north-west, and vanished, their fate unknown.
In fact, Borlin and the Legion made a successful assault against one of gates into Tethyamar, but ran into an orc-fashioned portal. This transported them deep into the mines, far from the entrance. Steadily, they fought their way through the orcs and back to the surface, but fell one-by-one. Borlin was the last, but he died in sight of Tethyamar's doors.
The Mithril Legion was led by Borlin, blood of Ghellin, Axe of the Iron House, of the exiled royal court of the Mines of Tethyamar.