Competition was key to the astonishing creativity of the Italian Renaissance. Nowhere was this truer than in Florence, where, in 1504, officials commissioned paintings by Leonardo da Vinci and Michelangelo for the Republic’s Great Council Hall. These murals are The Lost Battles (Knopf, $35) at the center of this rich account by The Guardian’s art critic, Jonathan Jones. Commissioned both to celebrate Florence and to determine who was the greater artist, the dual depictions looked to the past martial glory of Florence for their subject, but in approach and style pointed ahead to the art of the High Renaissance. As Jones defines the different strengths of the two competitors—Leonardo was “an artist who worked with ideas,” while Michelangelo was primarily a sculptor and dealt in risk and daring—he shows how these distinctions heralded new criteria for judging art. The emphasis was no longer on technical expertise, but on individual style and originality. And the winner? Neither artist completed the assignment, and the preliminary drawings were likely destroyed when the Medicis regained power in 1513.