Some 500 years ago, Sandro Botticelli, a painter of humble origin, created work of unearthly beauty. An intimate associate of Florence's unofficial rulers, the Medici, he was commissioned by a member of their family to execute a near-impossible project: to illustrate all 100 cantos of The Divine Comedy by the city's greatest poet, Dante Alighieri. A powerful encounter between poet and artist, sacred and secular, earthly and evanescent, these drawings...