This vessel depicts Medusa (headless on the left) and her two sister gorgons, right after the point where Perseus left with the monsters (i.e. Medusas) head. It is dated to ca. 620-610 BC.
"I [Perseus] thence arrived to where the Gorgon dwelt.
“Along the way, in fields and by the roads,
I saw on all sides men and animals—
like statues—turned to flinty stone at sight
of dread Medusa's visage. Nevertheless
reflected on the brazen shield, I bore
upon my left, I saw her horrid face.
“When she was helpless in the power of sleep
and even her serpent-hair was slumber-bound,
I struck, and took her head sheer from the neck.—
To winged Pegasus the blood gave birth,
his brother also, twins of rapid wing.”"
Ovidius - Metamorphoses IV
Translated by Brookes, M., 1922