Adorn

River in western Rohan, flowing westward from its source in the Ered Nimrais until it joined the Isen. (I 16; III 431)
The Adorn is a river who's headwaters began in the western heights of the Ered Nimrais/White Mountains. It flowed roughly north-westward to meet the Isen on the borders of Enedwaith. It was considered the western border of the country of Rohan, creating a long wedge of land reaching westward called The Westmarch.

The River Adorn is the only major tributary feeding into the River Isen in western Rohan. Its headwaters are fed by springs and snowmelt from the western heights of the White Mountains, called Ered Nimrais by the elves. As it descends from the highlands, the river flows roughly north-westward to meet the Isen on the borders of Enedwaith to the north.

The Adorn River was considered the western border of Rohan, forming a westward-reaching wedge of land the Rohirrim called the Westmarch. But this land, and lands west of the Adorn River stretching many leagues westward and reaching north to the Isen River were often contested between the Rohirrim and the Dunlendings.