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The Dead Peaks are appropriately titled as the mountain range is a magical dead zone. To be clear, there is no marked presence of abjurative or disjunctive magic but rather that that some natural influence suppresses magic and the supernatural of all kind and variety. Near the base of the mountain, the effect is weak. Near the peaks, it'll mute even legendary artifacts. Travel into the peaks and finding the invisible portal that leads to the Dead Peaks Prison puts one into a place where all life is dead and magic hasn't the will to rise whatsoever.
The reason behind this phenomenon is the subject of much speculation. One school of thought holds that that the locale is the literal and figurative 'peak' of the Shawnee Glacier recession, which some magical theorists propose will be the end of all magic, while some religious zealots entertain that it is an open wound in Gaia's belly. Another school of thought holds that while weakened magic and the effects of the dead zone are similar they are not related, and the cause of the phenomenon is the fact that the Dead Peaks were the birthplace of Zheng-yi the Witch-King. Zheng-yi is a necromancer of lore, written about in Terran history and arguably one of the strongest necromancer sof all time, born to a harlot and a psychopath on the brightest day of summer.
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