There are three types of armour un the arena Eternal. At the strat of a much, you won't have any, so you'll to look for it. Although the normal maximum armour rating you can have is 100, some improvements allow you to increase it beyond this limit, up to a maximum 200. Whenever your armour rating is above 100, it will gradualy count down until it reaches that mark, even if you aren't taking damage. Your current armour rating is displayed to the right of your character's face.