Weathertop, known as also Amon Sûl, was a hill in the Eriador region of Middle-earth, the southernmost and highest summit of the Weather Hills. The watch tower at its top overlooked the Great East Road in centralEriador, east of Bree, about halfway between the Shire and Rivendell.
As represented in the The Atlas of Middle-earth, the hill rose a thousand feet (approximately 300 meters) above the relatively level lands round about, and with only the lower Weather Hills stretching away northwards, offered a commanding view in every direction. A path led from the north side of Weathertop northward to the other Weather Hills. The elevation of Weathertop itself above sea level was likely in the order of 1500-2000 feet (around 450-600 meters)
History
The strategic importance of Weathertop was recognised early, and during the reign of Elendil the Dúnedain ofArnor built a watchtower on its summit, installing the most powerful of Arnor's three Palantíri in the tower. ThisPalantír further enhanced Weathertop's value, as it could be used for intelligence gathering and rapid communication with the King in Annúminas, or later in Fornost.
Left: Gil-Galad and Elendil meeting at Amon Sûl, by Abe Papakhian.
In TA 861, Arnor was divided into the kingdoms of Arthedain, Cardolan and Rhudaur. Weathertop stood at the junction of their borders, and became the focus of a long-running territorial dispute between the three kingdoms, with frequent border skirmishes and minor wars. During this time, Weathertop may have changed hands on several occasions. By the latter part of the 14th century, Weathertop was controlled by Arthedain and Cardolan, which were at that time allied against Rhudaur and Angmar, and was the chief fortress in their fortified border with Rhudaur. The watchtower and fortifications were burned and destroyed in TA 1409 by forces of the Witch-king.
King Arveleg I was slain while defending the watchtower, but the Dúnedain of Arthedain saved the Palantír and took it to their capital at Fornost. By the time of the War of the Ring only a ring of broken stonework remained of the watchtower.
source: http://lotr.wikia.com/wiki/Weathertop