Wall of Fire

{{spelldescription
 * icon=WallOfFire.png
 * type= Evocation (Fire spells)
 * level= Sor/Wiz 4
 * components= V, S, M (Heart of a Hen)
 * metamagic=Empower, Enlarge, Eschew Materials, Extend, Maximize, Quicken
 * range= Medium (100 ft.+10 ft. per caster level)
 * target= Foe, Positional, Breakable
 * duration= 10 seconds+1 second per caster level
 * save= None
 * sr= No
 * cd= 4 seconds
 * description=This wall deals 2d6 points of fire damage plus 1 point of fire damage per caster level (Maximum caster level 20.) to targets within the wall, and deals double damage to Undead creatures. The duration is 10 seconds plus 1 second per caster level.

Once the cooldown period expires, an additional firewall can be cast, so you can have multiple firewalls simultaneously.

Can ignite nearby wooden objects like crates and burns away webs. Like most persistant spells, will not function in water. Wall of Fire does not stack on top of other Walls of Fire. If Wall of Fire is touching another Wall of Fire that was cast previously, then first one is negated and does no additional damage.

This Level 4 spell (Abbreviated "FW".) is only available during leveling up, it cannot be purchased at a vendor.

Double Damage to Undead
}} Another theory: http://my.ddo.com/exalteddarkness/2010/07/01/wall-of-fire-a-theory-on-double-damage-vs-undead/