Expedition to Wave Echo Cavern
The Spellplague is a malady that struck on 29th Tarsakh, 1385 DR. Most Scholars believe that the Spellplague was caused by the death of Mystra, the goddess of Magic, at the hands of the god Cyric with the assistance of the Goddess Shar.
Other scholars argue that this cannot be the case, because Mystra has been slain before only to be reborn, and the Weave maintained its hold over the power of magic for the duration of her death. The truth will likely never be fully known to mortals, if it is even known to the gods.
With the goddess’s death, the Weave, the universal structure of arcane forces, convulsed. It continued for a decade, leading to the Wailing Years, during which time arcane magic ceased to function and the planet of Toril was transformed.