The River Isen (or Angren in Sindarin) began in the southern Misty Mountains, first flowing south through the fortress of Isengard (or Angrenost) to the White Mountains, where it abruptly bent west and flowed to the sea of Belegaer, the Great Sea.
Its length is about 430 Númenórean miles, making it the eighth-longest known river of Middle-earth.
Isen means Iron (cf. German eisen and Old English isærn = iron), Isengard meaning Iron fortress.
The Isen and Adorn formed the boundary of the Kingdom of Rohan, but the triangle of land between Isen, Adorn, and the White Mountains was a contested land, claimed by the Rohirrim as well as the Dunlendings.
The Isen formed a natural boundary in the Gap of Rohan, and was only crossable at Isengard or at the Fords of Isen, where the Rohirrim fought a number of great battles against the Dunlendings and Saruman's Orcs in the late Third Age.
|Settlements, Areas and Landmarks of Gap of Rohan|
|Settlements:||Grimbold's Camp • Forthbrond|
|Areas:||Wulf's Cleft • Isendale • Heathfells|
|Landmarks:||Âthdâr • Brôntrig • Cuvnerth • Dol Baran • The Pit of Iron • River-watch • The River Isen • Slave Stockades • The Smelters • The Sprawling Dark • The Underworkings|