The aegis is a shield carried primarily by Zeus in Greek mythology, which he sometimes lent to Athena. This shield is sometimes called a mirror and other times called a shield of bronze that was polished so much it reflected quite easily.
According to other sources, it was not a shield but rather an animal skin worn over the garments of the gods as extra protection. It bore the head of a Gorgon and made a terrible roaring sound during battle.
Along with being a very powerful shield, it is capable of radiating fear. It is finely polished, allowing one to look at their own reflection clear as day which also aids in deflecting powerful attacks. It can also turn people to stone, at least in its early use. It is said when a god shakes it, powerful thunder rolls, environments as large as mountains become wrapped in clouds, and mortals cower in fear.