Long ago, the first King of Arnor, Elendil, built the tower Amon Sûl in the center of his Kingdom, amid the Weather Hills. Its purpose was to house a palantír – one of the seven "seeing stones" through which Elendil, his heirs, and his liegemen could communicate with each other and watch over both the North and South Kingdoms.

In time, when Arnor broke apart into the three Kingdoms of Arthedain, Cardolan and Rhudaur, the sundered realms fractured around this tower, and their leaders often debated over ownership of the Weather Hills. All three Kingdoms desired control of the palantír, but eventually the lines of the Dúnedain in Cardolan and Rhudaur began to fail and Rhudaur fell beneath the sway of the Witch-realm of Angmar. During Angmar's first assault on Arthedain, the watchtower was razed to the ground; however, perhaps in preparation for such a day, the palantír had long been removed.