|Weathertop, as seen in Peter Jackson's The Fellowship of the Ring|
Following the death of King Eärendur in TA 861, Arnor was divided into three parts as a result of quarrels among his sons: Arthedain, Rhudaur, and Cardolan (S. ‘Land-of-Red-Hills’). Contained within Cardolan were the lands of Eriador between the rivers Baranduin and Mitheithel-Gwathló. On the border of Cardolan and Rhudaur lay the hill-tower of Amon Sûl (Weathertop), the possession of which would become a source of conflict for the two states. Arthedain, however, went from enemy to ally of Cardolan as a result of the growing threat of Angmar.
Throughout its history, Cardolan was frequently at war with Rhudaur, which had joined forces with Angmar. In 1409, forces from Angmar and Rhudaur crossed the border into Cardolan, surrounding Amon Sûl. The Tower of Amon Sûl was burned, Arthedain forced to retreat, and the Dúnedain of Cardolan had no choice but to seek refuge in Tyrn Gorthad (the Barrow-downs) and the Old Forest. It was during this war that the last prince of Cardolan was slain.
When Angmar was defeated by the Elves, the surviving people of Cardolan returned to their homeland. Not long after, the Great Plague struck in 1636, and the remaining population of Cardolan was lost, and the kingdom never reestablished, though there were small settlements still scattered throughout the land by the time of the War of the Ring.