In Greek mythology, the terrible Medusa with a head of snakes instead of hair had the power to turn anyone who looked at her into stone: a power that her head retained even when Perseus killed her by cutting it off.
The image (painted in the last decade of the 16th century) is set on a round shield, a "buckler" for use in tournaments, sent from Rome by Cardinal Francesco Maria del Monte as a gift to the grand duke of Tuscany Ferdinando I: Caravaggio's patron, the cardinal may have wanted to make the skill of his painter known in Florence as well. The choice of subject can be seen as a moral symbol of the victory of reason over the senses, and linked to a passage written by Ludovico Doke in 1565 that emphasized its function as a protection "against the wantonness of the world that turns men into stones."
Placed in the spectacular setting of the Medicean armory, the shield was held by a mannequin mounted on a wooden horse and dressed in an opulent Oriental suit of armor that had been donated to Ferdinando I by the legation of the shah of Persia, Abbas the Great.
After the explosion of the bomb in Via dei Georgofili in 1993, the work was subjected to examination and restoration that was also designed to arrest the constant process of deterioration to which it was subject.
Avoiding the frontal position of the head typical of theatrical masks, Caravaggio uses incident light to make the Medusa stand out, with an expression of horror and pain that reflects his studies from life. The staring eyes and mouth gaping in a blood-curdling scream fit the work into a series of extraordinary shrieking mouths stretching all the way from Leonardo's studies to Edvard Munch's Scream and the silent yell of Francis Bacon, inspired by Eisenstein's film The Battleship Potemkin.