Madonna del Parto (Pregnant Madonna) by Piero della Francesca (1415-1492)
For me her expression just exudes faith and trust. This is the most beautiful image of Mary I've ever seen. I came across it while on an art tour of Tuscany in the early 1990s, shortly before it was moved to a purpose built museum. At the time the fresco was situated behind the altar of a small church in the hill town of Monterchi. I feel very fortunate to have seen it before restoration,in all it's faded glory.