Barrier of Naach-Tith

This spell creates a powerful, yet desperate barrier that provides both physical and magical defense. Spells cannot be cast through the barrier either in or out. Any creature attempting to pass through the barrier must succeed a DC 40 Strength saving throw or deal 200 points of damage upon it, the barrier has a hardness of 10. If the save is successful, the barrier is destroyed instantly. Any hostiles creatures bisected by the initial cast are pushed outside of the sphere. Legend has it that the first written copy of this spell is located in a great haunted library on a planet in the astral plane, orbiting the star Celaeno in the Pleiades. For each level past 2nd this spell is cast, the sphere grows by another 10 feet. 

This spell is not class-locked. Any being able to learn the verbal and somatic components can cast this spell. The spell can be learned from a spellbook, a teacher versed in the spell, or from a deity. This spell is extremely rare, the few common folks who know this spell have had it mostly passed down through the family, considering the spells supposed alien origins.