Last year I travelled on a cruise from Rome down to Naples, across to Sicily and on to Malta, following the route taken by the sixteenth-century painter Caravaggio as he fled from justice after killing a man in a Roman street brawl. In each city the painter’s fame earned him commissions for portraits and altar pieces; dramatic scenes of martyrdom and miraculous interventions overflowing with life, his figures, barely contained within the frame, are lit with flashes of light that pierce the surrounding shadows. During my journey, while contemplating the play of light and dark that gives his paintings such…