What Role Did Medusa Play In History?

The Medusa, circa 1597, is an oil painting by the Italian Baroque master Caravaggio. It is in the Uffizi, Florence.
In Greek mythology, Perseus used the severed snake-haired head of the Gorgon Medusa as a shield with which to turn his enemies to stone. By the 16th century Medusa was said to symbolize the triumph of reason over the senses; and this may have been why Caravaggio's patron Cardinal Francesco Maria Del Monte commissioned him to paint Medusa as the figure on a ceremonial shield presented in 1601 to Ferdinando I de' Medici, Grand Duke of Tuscany - Del Monte was the Medici agent in Rome, and the Grand Duke was currently re-organising his personal armoury. The poet Giambattista Marino claimed that it symbolized the Duke's courage in defeating his enemies. In 1568 Leonardo da Vinci's biographer Vasari had written of a medusa-shield by Leonardo in the Grand Duke's collection. Leonardo's shield has since vanished, but if it existed in 1597 Del Monte would have known it, and in giving this commission to Caravaggio he was setting his protegé against the man recognised even then as the greatest of all painters.
As a feat of perspective, the picture is remarkable, for out of the apparently concave surface of the shield - in fact convex- the Gorgon's head seems to project into space, so that the blood round her neck appears to fall on the floor