Phalanx Fighting

 
Prerequisite(s): Base Attack Bonus 1+, Proficiency with Heavy Shield.
 
Benefit: If you are using a heavy shield and a light weapon, you gain a +1 bonus to your Armor Class. In addition, if you are within 5 feet of an ally who is also using a heavy shield and light weapon and who also has this feat, you may form a shield wall. A shield wall provides an extra +2 bonus to AC and a +1 bonus on Reflex saves to all eligible characters participating in the shield wall. For example, a single character with this feat gains a +1 bonus to his AC. If two or more characters who all know this feat are adjacent, they each gain an extra +2 bonus to AC (for a total of +3) and a +1 bonus on Reflex saves.
 
Special: A fighter may select Phalanx Fighting as one of his fighter bonus feats.
 
Source: Complete Warrior