You protect yourself from harm, your shield an extension of your body.

Prerequisite: Tower Shield proficiency, Improved Shield Bash

Benefit: The penalties to attack rolls for using a tower shield are reduced by 1, and you receive a +4 bonus to your CMD against attempts to sunder or disarm your tower shield. In addition, you can use a tower shield to make a shield bash as if it were a heavy shield, though it deals 1d6 damage for a medium sized creature on a hit.

Normal: You can’t shield bash with a tower shield.