In ancient times, the Witch of Izalith attempted to recreate the First Flame with the Lord Soul that was in her possession. Instead, she spawned a corrupted fire known as the Flame of Chaos. When she failed to control the new flame, it consumed her and molded her into a twisted being known as the Bed of Chaos, the source of all demons.
Eventually, the Bed of Chaos was destroyed by the Chosen Undead, but the flames of Chaos lived on. At an unknown point, the flames of Chaos were discovered deep below the kingdom of Eleum Loyce. In an attempt to appease the raging flame, the Ivory King built a great cathedral at its mouth and the oracle of Eleum Loyce, Alsanna, prayed in silent vigilance. The attempt was unsuccessful and the flames still raged.
The king made some attempts to combat the Chaos, and his knights delved valiantly into the depths to exterminate the terrible things that dwelled there, but not one of them returned. Eventually, the Ivory King sensed the degradation of his soul and left Eleum Loyce. He traveled deep into the Chaos with his knights until he was devoured by the flames.
The Old Chaos appears as a large circular platform afloat a sea of lava. It is accessed by progressing through the DLC until Alsanna, Silent Oracle is met, at which point she will open up the passage that leads there. After passing through a fog gate, the player drops down a deep pit which deposits them onto the platform. At least one Knight of Eleum Loyce will accompany the player into the Chaos.
Upon arrival, Charred Loyce Knights will begin to appear from the portal gates at the edges of the platform. After several of them have been defeated, large pillars will raise from the lava and the Burnt Ivory King will enter the arena to initiate the final boss battle. After he has been defeated, a beam of light will appear at one end of the platform to warp back into the cathedral.
After the king's defeat, the Old Chaos can be continually be accessed to fight Charred Loyce Knights and obtain Loyce Souls for Alsanna.