Castle

A card type first introduced in the DM-30 Ultra Duel set. A Fortress is put into the Shield Zone equipped to a shield, now forth called a "fortified shield". As long as the fortified shield remains in the Shield Zone; the Fortress' ability will be in effect. When the fortified shield leaves the Shield Zone, the Fortress is put into the Graveyard. However you can still used the Shield Trigger ability of that shield. Keep in mind that you can equip more than one Fortress to a shield, but some cards encourage one Fortress per shield by having additional effects when being the lone Fortress attached.