The Sea of Souls is the name of the protective sea-wall built around Stygia and the Isle of Sorrows. Its name comes from the unfortunate wraiths who have been forged or chained into the wall's structure. Augmented with Stygian steel, those wraiths are little more than Drones who are chained to the wall's surfaces and drift along with the flow; their Corpus has a water-like consistency that lets the wraiths imprisoned there slide past one another easily. Their groaning and cries are easily heard by those traversing over the Sea of Souls. However, their binding to the wall keeps them from feeding Oblivion, providing an emotional barrier for Stygia as well as a physical one.
The Sea of Souls was put into place by Charon following the near-destruction of Stygia in the First Great Maelstrom. The legendary Weeping Bay which also became a major part of Stygia's history is part of the Sea of Souls.