The name given to the southerly regions of Arnor, between the rivers Baranduin and Gwathlo. Cardolan was a roughly rectangular land, running southwestwards from Amon Sul to the shores of the Great Sea. Its shoreward parts were known by the name Minhiriath, the land 'between two rivers'.
The name Cardolan seems to have been used from early in Arnor's history, but after the death of King Earendur of Arnor in III 861, it became a kingdom in its own right. At that time, Earendur's sons divided the North-kingdom between them, and Cardolan's first king appears to have been Earendur's second son, whose name history does not record.
During the early part of Cardolan's history, it vied with the neighbouring lands of Arthedain and Rhudaur over the control of the Tower of Amon Sul and its palantir. At this time, at least part of Cardolan's northern border with Arthedain was fortified by a hedged dike and wall, the remains of which survived to the time of the War of the Ring.
As the centuries passed, the threat of the Witch-king's realm of Angmar turned Cardolan and Arthedain from rivals into allies, and they fought together against Angmar and Rhudaur (which had become a client state of the Witch-king). Together they maintained a joint defence that ran along the Weather Hills and the upper River Mitheithel.
In the year III 1409, the Witch-king mounted a decisive assualt against these defences, crossing the Mitheithel into northeastern Cardolan. The Tower of Amon Sul was destroyed, though its palantir was saved. The armies of Angmar and Rhudaur went on to ravage Cardolan's lands, and slew the last prince of its royal line. The surviving Dunedain retreated into the Barrow-downs and the Old Forest, which lay on their northern borders.
After this time, with the loss of its royal lineage, Cardolan was no longer properly a kingdom. Nonetheless a band of Dunedain endured in the downs and the forest for more than two centuries, until the coming of the Dark Plague. The last of the Dunedain, and most of the land's other inhabitants, were lost to the Plague, and as a final blow the Witch-king sent evil beings to infest the Barrow-downs. After these events, Cardolan was left a desolate and deserted land.