Blade barrier

Blade barrier is an evocation spell that summmons a ring of spinning blades.

Effects
This spell creates a spinning disk of razor-sharp blades. These whirl and flash around a central point, creating an immobile, circular barrier. Any creature passing through the blade barrier takes 1d6 points of slashing damage per caster level (maximum 20d6). The plane of rotation of the blades can be horizontal, vertical, or slanted.

Creatures within the blade barrier when it is invoked take the damage as well. They can negate the damage with a successful Reflex saving throw, provided they can and do physically leave the area of the blades by the shortest possible route. Once the barrier is in place, anything entering or passing through the blades automatically takes damage.

A blade barrier serves as one-half cover (+4 AC) for anyone beyond it.