The story of Swamp of Sorrows.
The Swamp of Sorrows is a dark, wet marsh of hanging moss, black water and crocolisks north of the Blasted Lands. Together they were once one great marsh, the Black Morass; after the Second War the northern half was renamed for the war's countless dead, and the name has stuck.
The swamp holds one of the darkest places in the Eastern Kingdoms. After the fall of the Gurubashi Empire, the Atal'ai, troll priests devoted to the blood god Hakkar, fled here and built a temple to summon him into the world. The Dragon Aspect Ysera saw what they were doing and drowned their temple in the bog. The Temple of Atal'Hakkar lies there still, half-sunken in a lake in the middle of the swamp, guarded by green dragons under Eranikus, and the Atal'ai inside have not given up.
The Horde has held the swamp longer than almost anywhere in the Eastern Kingdoms. Stonard, in the south-west, was an orc base during the First War; it was nearly destroyed, but the Horde has rebuilt it, and today it is their stronghold in the south. Elsewhere in the marsh live the Lost Ones, broken draenei driven mad by their long exile from their homeworld, and the swamp's own creatures, none of them friendly.
Written for this site from the game's lore. Further reading: Swamp of Sorrows on Warcraft Wiki.

