rek10354 said:

how do you protect your citadel from attack,are there shields for citadel?

Essentially ... you don't.

The Citadel is only attackable if you have announced a championship. You do so so you can get points from killing the (foreign) troops that attack it. (Which you no doubt know.) Therefore, to protect your citadel from attack, don't announce a championship. i.e. The only reason to announce a Championship is because you want your Citadel to be attacked.

However, to not lose troops (in between the foreign troop attacks), you must withdraw them from the Arena. There is no way to shield the Citadel. (An 8h shield would last longer than the Championship ...)