The adamant defender is a defender made out of adamantite and can be obtained by killing Cyclopes on the top floor in the Warriors' Guild, but only if you have acquired the Mithril defender first. It is held in the shield slot, and requires 30 Attack and 30 Defence to wield. It is recommended to keep the adamant defender as a backup in case a player were to lose their rune defender and having no other defenders would have to start back at bronze. Collecting more than one rune defender however solves this problem.
If the player dies below level 20 Wilderness, it will remain in the player's inventory. However, the item will be unusable and must be repaired with 25,000 coins by using the item on Perdu.