Shield of the Besieged Tower
Swordmage Utility 16
The more foes stand arrayed against you, the stronger your defensive magic is.
Personal
Effect: Until the stance ends, you gain a +1 power bonus to AC. If at least two enemies are within 3 squares of you, this bonus increases to +3.
Shield of the Besieged Tower is a daily power available to swordmages at the 16th level.[AP:59]