Greek / Roman Mythology
The Aegis is a protective device that was carried by the God Zeus (Jupiter), and was often lent to his daughter Athena (Minerva).
The word aegis derives from the word for "goat skin", and comes from the shields of tanned goat skin that warriors in Ancient Greece would carry.
It is usually represented as either a shield, or some sort of cloak, made out of goat skin, with golden tassels. Specifically, the aegis was said to have been made out of the skin of the she-goat Amaltheia (Amalthea?), who protected and suckled Zeus as an infant, before he overthrew the Titans, freeing his siblings from the stomach of his father Cronus, who had eaten them upon birth.
The shield aegis was made by the god Hephaestus, and covered with the skin of Amaltheia.
The aegis was indestructible, and offered whoever had it ultimate protection. It inspired fear and awe in your opponents, and when Zeus shook it, it produced thunder. It also allowed one to protect those you were friendly with.
When Perseus had to slay the Gorgon, Medusa, he was assisted by Hermes and Athena. Of course, it was also Athena who has originally transformed Medusa into a hideous beast. Athena was just pissed off because Poseidon had ravished Medusa in her temple, desecrating it.
Anyhow, in gratitude for Athena's help, Perseus gave Athena the severed head of Medusa, which she took and placed in the center of the aegis. She is often depicted wearing it like this, with the former golden tassels replaced with four snakes, supposedly representing fear, flight, force, and pursuit.
The aegis was later used at the battle of Troy, according to the Iliad. Apollo and Athena were watching the battle, Apollo very much on the side of the Trojans, after the Achaeans insulted one of his priests.
Hector was in the battle, and was wounded by Aias. This pissed off Apollo, so he took the aegis and used it to drive the Achaians off the battlefield, fleeing to their ships.
This didn't save Hector, who was eventually killed by Achilles.