“The 20-man raid, River of Souls is now open!” Trion Worlds announced. “Prevent Alsbeth the Discordant’s plans to reanimate the most powerful souls to fight in the army of Regulos.”
River of Souls originally was introduced to the game as part of a world event in March 2011’s Update 1.1. Players might recall that this first world event didn’t go as great as anyone had hoped, generating no small amount of controversy at the time.
Source: RIFT. Thanks Anon!