Some five hundred years ago, Sandro Botticelli, a painter of humble origin, created works of unearthly beauty. A star of Florence's art world, he was commissioned by a member of the city's powerful Medici family to execute a near-impossible project: to illustrate all one hundred cantos of The Divine Comedy by Dante Alighieri, the ultimate visual homage to that "divine" poet. This sparked a gripping encounter between poet and artist, between the religious...