A Chaotic Zone is a systematic feature exclusive to Tales of Legendia.
Chaotic Zones are large purple and black domes that appear in dungeons, representing a dangerous area. Within these zones, the enemy encounter rate raises significantly, and the enemies encountered within them are likewise stronger than typical enemies of the area. Once the battle is over, the Chaotic Zone will disappear. Systematically, Chaotic Zones are typically employed to protect optional treasure chests and can usually be avoided entirely.
During the story, Senel Coolidge and Will Raynard first encounter a Chaotic Zone at the entrance to the Misty Mountains, where Will explains that Chaotic Zones are places that teem with the spirits of monsters and citizens tend to avoid them if at all possible. He also explains how treasure hunters and Erens will typically rush into them, seeing only the treasure chest that lies beyond.