The Dead Men of Dunharrow

At Erech stands a black stone brought, it was said, from Númenor by Isildur, and on that stone the King of the Mountains gave him his allegiance in the first days of Gondor's realm. When Sauron rose again, Isildur called on the Men of the Mountains to keep what they had sworn, and they refused: their worship in the Dark Years had gone to Sauron. Isildur's answer to their king was a sentence of doom — that he would be the last ever to rule them, and that should the West outmatch his Black Master, neither he nor his people would find rest until the oath was kept. They fled before his wrath, did not dare go to war on Sauron's part, hid in secret places and slowly dwindled in the barren hills. Aragorn called them at the Stone: Oathbreakers, why have ye come? And a voice answered out of the night, to fulfil our oath and have peace. Their kindred were the folk who in far older days had their homes in the valleys of the White Mountains.