This powerful spell is designed to prevent unauthorized spellcasters from entering a hallway, doorway, window, or other point of entry.
The spell creates an invisible barrier that blocks the targeted area. Any nonspellcasters and those spellcasters specifically named by the caster may pass freely. All other spellcasters collide with the invisible barrier. Members of classes with lesser spellcasting abilities (paladins, rangers, and bards) are blocked only if the character is of sufficient level to cast spells.
The wizard is able to ward one area up to 20'-square for each level of his experience. Thus, a 12th-level wizard may protect a square area 240 feet on a side. The area of effect may be divided among several smaller portals as long as the total area does not exceed the caster's limit. Each portal must be in range and sight of the caster at the time the spell is cast.
The barriers exist for one hour per level of the caster unless they are dismissed by the caster or dispelled by a dispel magic spell. A disintegrate spell immediately destroys a barrier, as does a rod of cancellation or a sphere of annihilation.
The invisible walls are not affected by physical blows, cold, heat, or electricity. Thrown and projected weapons (both magical and mundane) are not repelled by the barrier and may pass through the area normally. Spells can be cast through the barrier. Dimension door, teleport, and similar effects can bypass the barriers.
The material component is a pinch of dust from any wizard's tomb.