Athena and the Aegis

Medusa was killed by the hero Perseus with the help of Athena and Hermes. He killed her by cutting of her head and gave it to Athena, who placed it in the center of her Aegis, which she wore over her breastplate.

The Aegis is a protective device that was originally associated with Zeus, but also, and later solely, with Athena. It is variously considered to be a bright-edged thundercloud (because when Zeus used it lightning flashed and thunder sounded) fashioned by Hephaestus, or the skin of the divine goat Amaltheia. It is represented as a sort of cloak, sometimes covered with scales and fringed with serpents, and with the head of Medusa fastened in the middle. The Aegis could also serve as a shield and in that fashion Athena wears it upon her breastplate. 

This statue of Athena from the old Parthenon, now in the Acropolis Museum, shows her snaky aegis well.