The River Iss is the sole remaining river upon Barsoom. For ages, Green and Red Martians took a pilgrimage to the river upon their thousandth year of life to what they believed was the afterlife.
Description[]
One part of the river empties into the Valley of Lost Souls, and the islands in the valley are covered in the corpses of Red and Green Martians who abandoned their attempt to journey down the river.
Those who completed their river journey find no paradise. The lost sea of Korus lays at the end and plant men and white apes await them as prey. If they do not meet their ends at the hands of the apes and/or the plant men, they are likely taken by the Therns to be enslaved or used as a food source.