Prydwen

Origin
Prydwen was a shield contained in the vaults of Camelot that was passed down to every king who ruled there. Where or how it was created is unknown. It became the shield of King Arthur.

Abilities
Prydwen has an immunity against conventional weaponry, decided by the knowledge and acclaim of that weapon. The more well known a weapon is and the more fame it has as a deadly weapon, the less powerful it would be against the shield. A more obscure weapon with less acclaim would be more effective against the shield. The effect only works for the type of weapon, and does not consider the specific item. For example, Excalibur or Caliburn would both do the same amount of damage as a normal sword against it.

The shield works by crystallizing knowledge into its own physical form. If enough knowledge of an item is held, that knowledge will increase the density of the shield. However, if not enough knowledge is held, the shield will fail to crystallize a defense and the weapon will go straight through, doing only slightly less damage to the target. The shield is not damaged when this happens, which renders the shield technically indestructible.

Power
Prydwen could theoretically completely block out nuclear bombs or even life ending asteroids due to humanity's fear of them leading to everyone knowing of them. However, it would be completely useless against an extremely obscure weapon that could barely even kill a human.