Your mastery of the tower shield makes it impossible to catch you off guard.
Benefit: If you successfully hit at least one shield bash attack with your tower shield when making a full-attack action, you can use a swift action to grant yourself total cover on one edge of your space. If you spend a move action to place your tower shield (with the Archon Defense feat), you can choose two contiguous sides of your space to defend, rather than just one. Changing which side you are defending using the Archon Defense feat changes both sides with the same action.
Path of Iron, © 2015, Ascension Games, LLC; Author Christopher Moore