Some of the underlying tensions—I hesitate to use the word conflicts—in this ambitious book are expressed even before it is opened, in the juxtaposition of the name of the great Florentine artist, Giotto, with a detail of the Virgin and Child from the Rucellai Madonna painted by the Sienese master Duccio on the cover. Is the point that the era belongs (or has belonged) verbally or nominally to Giotto (i.e., Florence), but, in fact, visually...