This is a huge ice-scarred boulder, and traditionally it is held that the Gaelic bard Ossian was buried here.
Funnily enough, though, it may have marked the grave of someone previous even to Ossian. Seton Gordon writes in his "Highways and Byways in the Central Highlands", quoting from an earlier source of the moving of the boulder by General Wade's road-making soldiers:
"There happened to lie directly in the way an exceedingly large stone, and as it had been made a rule from the beginning to carry on the roads in straight lines, as far as the way would permit, not only to give them a better air, but to shorten the passenger's journey, it was resolved the stone should be removed, if possible, though otherwise the work might have been carried along on either side of it.
The soldiers, by vast labour, with their levers and jacks, or hand screws, tumbled it over and over, till they got it quite out of the way, although it was of such an enormous size that it might be matter of great wonder how it could ever be removed by human strength and art, especially to such as had never seen on operation of that kind; and upon their digging a little way into that part of the ground where the centre of the base had stood, there was found a small cavity, about two feet square, which was guarded from the outward earth at the bottom, top and sides, by square flat stones.
This hollow contained some ashes, scraps of bones, and half-burnt ends of stalks of heath; which last we concluded to be a small remnant of a funeral pile."
There follows some speculation that it was a Roman officer... Gordon also quotes from the Ordnance Gazette, on what happened afterwards:
"The people of the country, to the number of three or four score men, venerating the memory of the bard, rose with one consent, and carried away the bones with bagpipe playing and other funeral rites, and deposited them with much solemnity within a circle of large stones, on the lofty summit of a rock, sequestered and difficult of access... in the wild recesses of Glen Almond.
Wordsworth wrote a poem about Ossian's grave. So maybe it was this one he knew - or maybe the Clach Ossian down the road. Who knows. If you read the poem, Wordsworth isn't sure whether Ossian's here or not either - it's the atmosphere of the glen that's important. So maybe it doesn't matter.
Glen Almein, or The Narrow Glen.
In this still place, remote from men,
Sleeps Ossian, in the Narrow Glen;
In this still place, where murmurs on
But one meek streamlet, only one:
He sang of battles, and the breath
Of stormy war, and violent death;
And should, methinks, when all was past,
Have rightfully been laid at last
Where rocks were rudely heaped, and rent
As by a spirit turbulent;
Where sights were rough, and sounds were wild,
And everything unreconciled;
In some complaining, dim retreat,
For fear and melancholy meet;
But this is calm; there cannot be
A more entire tranquillity.
Does then the Bard sleep here indeed?
Or is it but a groundless creed?
What matters it? I blame them not
Whose Fancy in this lonely Spot
Was moved; and in such way expressed
Their notion of its perfect rest.
A convent, even a hermit's cell,
Would break the silence of this Dell:
It is not quiet, is not ease;
But something deeper far than these:
The separation that is here
Is of the grave; and of austere
Yet happy feelings of the dead:
And, therefore, was it rightly said
That Ossian, last of all his race!
Lies buried in this lonely place.