In the fiction of J. R. R. Tolkien, Weathertop (Sindarin Amon Sûl, "Hill of Wind") is a significant hill in the Eriador region of Middle-earth, the southernmost and highest summit of the Weather Hills.
Weathertop overlooks the Great East Road east of Bree, about midway between the Shire and Rivendell. The hill rises a thousand feet above the level lands round about, and was the site of a watchtower in the days of Arnor. The watchtower and fortifications were burned and destroyed in , but the top is still flat and surrounded by a ring of stones. A path leads from the top northward, connecting to the other fortresses of the Weather Hills. The tower originally held one of the seven palantíri.
Weathertop is not mentioned in The Hobbit, but is a scene of action in The Lord of the Rings. After fleeing from Bree, Strider and the hobbits avoid the main road and approach Weathertop from the north. At the top they discover a cairn with a message from Gandalf, and see the Ringwraiths approaching in the distance along the road. That night, the Ringwraiths attack their camp in a dell below the summit, stabbing Frodo with a Morgul-blade, but are then driven off by the others.
When Arnor was divided into three kingdoms in 861 of the Third Age, the Tower of Amon Sûl was claimed by Arthedain and commanded the east road into Rhudaur from Cardolan. Also a special warden was posted there to guard and maintain the palantír. But Cardolan and Rhudaur also wanted possession of the Tower and its seeing-stone and there was strife among the three kingdoms.
In 1356, King Argeleb I of Arthedain was slain defending the Weather Hills against an assault from Rhudaur, which was then ruled by an evil lord of the Hillmen who had secretly joined forces with the Witch-king of Angmar. Arveleg, son of Argeleb, drove back the invaders and defended the Weather Hills for many years. But in 1409, Weathertop was surrounded by a great host from Angmar. Arveleg was killed and the Tower of Amon Sûl was burned and razed. The stone (Palantir) of Amon Sûl was rescued by the forces of Arthedain, but it was later lost at sea.
Over time the ring of stones that had once been the foundation of the Tower of Amon Sûl crumbled and became overgrown with grass. When Gandalf came to Weathertop on October 3, 3018, he was besieged by the Nine Ringwraiths in the ruins. There was a great battle on the hilltop, and when he escaped Gandalf left a cairn of broken and burned stones in the centre of the ruins. Gandalf marked the topmost stone with the G rune and three strokes to indicate that he had been there on October 3. Aragorn interpreted the message when he came with the Hobbits to Weathertop on October 6. Later that night in a dell on the western side of Weathertop, five Ringwraiths attacked and Frodo Baggins was gravely wounded by the Witch-king before the Ringwraiths withdrew and Aragorn led the Hobbits away.