Defensive buildings allow you to significantly improve the defensive ability of Units protecting your Castle.
Gates and Walls are basic elements that affect your Castle’s protection. By improving your Gates, you automatically improve the strength of your Walls as well.
You can also place special Units on dedicated slots along your Castle Walls, within the Castle itself, and even just outside of your Castle Walls. In case of attack, these Units will fight like regular Defensive Units and aid you in Defense of your Castle. However, if the enemy prevails, these Units will only be out of action temporarily, and can be revived in less than 2 hours. Simply tap on them to revive them.
To improve your Defensive buildings, upgrade the Lost Art of Fortifications.