One of the most beautiful man-made places on earth: Piero's frescos in the Cappella Maggiore in the church of San Francesco, Arezzo (Alinari Archives/George Tatge/Getty)

It seems incredible that so tediously mediocre a painter as Bicci di Lorenzo could ever have been preferred to Piero. But perhaps what displeased, or at least did not excite, clerical patrons in the 15th century may have been the element that appeals to us today: the unclear, almost ambiguous, nature of Piero's religious faith.

Piero depicts religious subjects. But he does not do so in an overtly religious way: he does not do religious propaganda, as most of his 15th century contemporaries did. The heart tends to sink at the prospect of a gallery filled with a long sequence of gold-backed Virgins and saints being martyred. Piero's pictures never have that lowering effect, and they always stand out from any crowd of gilded Annunciations or martyrdoms. While they depict incidents that are part of the Christian religion, they also convey the sense that illustrating the truths of the Christian religion is not their real point. As the great (although occasionally perverse) Italian critic Roberto Longhi wrote in his essay "Piero in Arezzo", Piero's Legend of the True Cross frescos "refer only minimally to the ‘religious' core buried within each scene. Instead, we have what looks very much like an extensive epic of secular, profane life."