Advance
Defensive Mentality
There are those who think that attack is the best form of defense, but that is foolish. Let our enemies come to us instead; we shall counter with incredible zeal. Our troops will defend their homes tenaciously, and our fortresses will withstand sieges for longer.
Advance tree
The game files don’t say where this goes: it has no requires, so the game places it in the 
Reformation tree itself.
Modifiers
Fort Defense+20%