Mystra's Ban

Mystra's Ban was a decree that the goddess Mystra made about the mortal use of powerful magic.

History
Before Mystra's Ban, there was no practical limit to the ways magic could be used. Any being with enough skill, intelligence and willpower could use magic, with very little effort. Beings could tap the Weave directly and use its magical energy. There was no limit on the amount of magical power that could be channeled into a spell.

The ban was enacted only moments after the Fall of Netheril caused by Karsus's Folly.

Outcome
The first effect of the ban was to limit spellcasting to spells of a maximum of 9th level, with some special Epic Spells being more powerful than that. The second effect was that all spellcasters had to spend time memorizing spells and were limited to holding a certain number of magical spells in their head at any one time.

Epic magic was not affected by Mystra's Ban.