A fortress city of the Northern Dúnedain, situated at the southern end of the range of hills known as the North Downs, at the northern end of the great North-South Road that led to distant Gondor and the South-kingdom. The city's name translates literally as 'northern fortress', but is also translated by the equivalent 'Norbury' (or, in full, Fornost Erain, 'Norbury of the Kings').

During the early history of Arnor, Fornost was an important city, but not the capital of the High Kings. They ruled from Annúminas on Nenuial, about a hundred miles to the west. It was only after the breakup of the North-kingdom into three lesser realms that Fornost became a seat of Kings. Amlaith son of Eärendur, first of the Kings of Arthedain, established himself here, and indeed is known to history as 'Amlaith of Fornost'.

The history of Arthedain was one of almost constant warfare against Angmar and its allies. In the year III 1409, an immense attack from Angmar saw the destruction of the Tower of Amon Sûl that guarded Arthedain's borders, but the palantír held there was rescued and taken back to Fornost. From this time both the active Stones of Seeing held by the North-kingdom were at Fornost.

The Kings at Fornost held against Angmar for nearly six more centuries, but in III 1974 the Witch-king of Angmar finally succeeded in breaching the city's defences, driving out its people and filling Fornost with his own followers. The last King of Arthedain was Arvedui, who fled from Fornost with the palantíri, but was lost in the cold northern seas.

The Witch-king would not hold Fornost for long. In the following year, Eärnur of Gondor led a force northwards that not only avenged the North-kingdom by driving the Witch-king out of Fornost but, in a climactic battle, overthrew Angmar itself. Though their enemies were now destroyed, the Northern Dúnedain were too diminished to re-establish the city.

After this time the former inhabitants of Fornost became a wandering people, and Aranarth son of Arvedui became the first Chieftain of the North, rather than King of Arthedain. Fornost itself fell into ruin and decay, and in the thousand years that followed, it became a forgotten and ruinous place, little visited except by the Rangers, and known to the peoples who lived nearby as 'Deadmen's Dike'.

The fate of Fornost after the War of the Ring is uncertain, but after Aragorn established himself as a new High King of a Reunited Kingdom, the Wizard Gandalf predicted that it would once again be visited by the King, suggesting that at some point it would be refounded by the Dúnedain.³