At the first we stood high on the slopes,
-No real idea where to start here except that there is a 'we' so it's clearly multiple individuals or things.
Watching waiting as the wanderer climbed.
-Wanderer makes me think of Gandalf or Aragorn but it could be a host of people from the Silmarillion
One of us watched the dance in the dark,
-I can't recall if there's a 'dance' with Gollum or another in the dark, so it could mean combat. This makes me think of Gandalf fighting the Balrog
Held the haggard hero lest he fall.
-First thought is Samwise holding Frodo, but in looking at previous I can make the argument of Gandalf again, however it's 'we' not I...so?
And one strode swift through gentle hills,
-No real clue on this one
Great gait drawing the gaze of passer-by.
-Same, no idea
But at the last we fell, frail and weak:
-This one gives me pause, because what other plural failed other than all the ringbearers which it isn't that answer? The 9 kings of old failed and became wraiths...but the other clues don't hold up to that.
The master may have mourned us, if he learned.
-This one, led me first to think of Frodo and Gollum but I think there's more to it. The Master ring is the only other thing that makes sense. If it failed after the master wouldn't have learned it makes me think that maybe it's....
The 3 elven rings?