Dome of Corruption

The caster seals a pact with Horrors. The Horrors create a dome that protects the province from most spells that originate from outside the warded province. Trying to cast a spell through this dome is very dangerous and might drive the casting mage insane. A good side effect of the dome is that it exudes magic and will raise the magic scales of the province considerably, making it easy for mages to do their research. The pact has a downside too, which will become apparent to mages living under the dome. The creators of the dome will occasionally attack and consume a mage. The dome will dissolve instantly if the caster of this ritual dies.

Text: Illwinter Game Design, via Dom6 Inspector