An impassable rapids on the river Anduin's course through the Emyn Muil just north of the ancient border of Gondor. A portage-way was constructed along the western bank of the Anduin to allow boats to pass the rapids. This portage-way ended to the south at a small pool scooped out of the bank by the current. Travelling from this pool it was less than a half days journey to the Argonath and Nen Hithoel.

It was in the northern approaches to the Sarn Gebir that the Fellowship was attacked by orcs firing arrows from the eastern bank.
Encyclopedia entry originally written by PotbellyHairyfoot