The River Agis flowed from the east out of the Marching Mountains and into the Trackless Sea near the city of Memnon.[1] The river was called the Memnon River in most of Tethyr.[2]

It served as the border between Calimshan and Tethyr ever since the Eye Tyrant Wars.[1]

The river was wide and slow-moving and very suitable for cargo-carrying barges and lumber.[1] However, it did not receive as much traffic as would be expected owing to fears regarding Shoonach,[2] as Port Agis, a section of Shoonach, also lay along the river upstream.[3]