You form a unified defense with those around you.
Prerequisite: Shield Proficiency.
Benefit: Whenever you are wielding a shield and are adjacent to an ally wielding a shield who also has this feat, the AC bonus from your shield increases, depending on the shield wielded by your ally.
You keep these bonuses even if your ally loses his shield bonus due to making a shield bash attack.
If an adjacent ally with this feat uses a tower shield to grant total cover, you also benefit if an attack targeting you passes through the edge of the shield.