Line of Protection

This cooperative spell requires at least two priests to cast the spell simultaneously. During the casting, the priests determine whether the line will be stationary or portable.
If the spell is stationary, each priest must inscribe a magical sigil on parallel facing surfaces, such as facing walls of a gatehouse or two tree trunks. If the spell is portable, the priests must stand at each end of the line, thereby anchoring it. After the spell is cast, a shimmering field of force appears between the two anchors (the sigils or priests). The field is 10 feet high and sparkles with energy. Objects on the opposite side of the translucent field, while recognizable, are hazy and indistinct.
The field causes 1d3 points of damage to all creatures passing through it; evil creatures and undead suffer 1d8 points of damage from the field. Creatures that roll a successful saving throw suffer no damage. Creatures that can fly over the field, burrow under it, or Teleport to the other side are immune to damage.
If the spell is cast in its portable form, the priests can move at half their movement rates (limited to the rate of the slower priest). The priests can take no other action, since all their energy is spent in walking and maintaining the field.
Once created, the field cannot be increased or decreased in length and must remain straight. The priests could maneuver by pivoting, but could not walk toward each other or bend the field around a corner. If the line of sight between the two priests is blocked by any object of greater than 5' diameter, the spell immediately fails. Thus, creatures, low walls, young trees, pillars, and similar objects will not disrupt the spell. As a cooperative spell, several priests can link together to create a longer field. Each priest (or sigil) forms the end of one field and the beginning of another, much like fenceposts. Each section of the spell must extend in a straight line, but the field can be bent at each junction. Four priests could form a long line, a square, or a Z pattern. The restrictions on moving the fields apply as outlined above. The DM may apply movement penalties depending on the complexity of the pattern. The material components are held aloft by each caster.

Reverse: Line of Destruction

The reverse of this spell, line of destruction, causes 1d3 damage to all creatures passing through it. It causes 1d8 damage to paladins and creatures of good alignment who pass through it. Creatures that roll a successful saving throw suffer no damage.

[Tome of Magic]

Reversible

Sphere: Protection
(Abjuration)
Level: 3
Cooperative

Range: 0
Components: V, S, M
Duration: 1 round/level
Casting Time: 1 round
Area of Effect: 30-yard line
Saving Throw: Negates

Material Components:
the priests' croziers, staves, or religious standards