An aegis was a leather cloak, breastplate or shield. Athena placed the head of Medusa at the center of her aegis.
This cup shows Athena on the right with the Medusa on her aegis. On the left is the dragon that guarded the Golden Fleece. He is in the process of disgorging the hero Jason who had been sent to fetch the Golden Fleece, which is hanging on a branch above.
Jason had set off with his band of heroes known as the Argonauts because the ship they sailed in was called the Argo. After various adventures in the ports of call along the way to the eastern ends of the known world, at the edge of the Black Sea, in Colchis, Medea, daughter of the king who owns the fleece, falls in love with Jason and helps him get the fleece away. She does this despite the fact that it is a betrayal of her family. As a result, though, Medea has to flee with Jason and the Argonauts when they leave Colchis.
The aegis comes from the head of Medusa. Athena had helped the hero Perseus to slay the Medusa, but the head of Medusa was too powerful for Perseus to keep, so he gave it to his benefactor, Athena.
