The River of Pain (Paludia supplement)
From D&D Wiki
The River of Pain is located deep in the heart of Paludia, and is over 250 kilometers to the north of Lixus. It is often considered to be the dividing point between the relative civilization of Lixus and its neighbors, and the wild lands to the north. While countless other wild areas exist in Paludia which are very far away from the River of Pain, there is no better example of a natural boundary which separates wilderness from civilization (or for what passes for civilization in Paludia.)
The River's name is well-earned, as it has been the site of many battles between Lixius's armies and hostile tribes to the north.