While trapped in Regina I had the opportunity to watch 'The Power of Art', a program from the BBC (naturally) that walks us through some of the great artists, their lives and most importantly, their work.
The first episode on Carravagio was nothing short of riveting, and the story of his life literally comes to an end with the above painting of David and Goliath.
After having killed a man in a duel, Carravagio flees Rome for distant parts of Italy to stay ahead of the bounty that has been placed on him. When it eventually reaches him that he has a patron seeking his pardon with the Pope, he paints the above. In it, David holds the head of the slain Goliath - but more interestingly, is Goliath's visage - Carravagio gives Goliath his own face.
It's a joke, but very dark one - he is in effect saying to his patron, 'There is a price on my head - so here, I offer it to you'.