Late in the spring of 1349, Petrarch, famous for his lyrical cries for peace on the Italian peninsula, wrote the priors of Florence urging the city to war. Two of the poet's dearest friends had been attacked while passing through the mountainous terrain controlled by the rural Ubaldini clan, renegade Ghibellines who menaced crucial trade routes between Florence and Bologna and were taking advantage of Florence's vulnerability in the wake of the 1348 outbreak of the Black Plague. The two campaigns that Florence launched against the Ubaldini, one in 1349 and one in 1350, although little known (overshadowed by the plague on one side and, less so, by the 1351–1353 Florentine war with Milan on the other), are better documented than any contemporary war and, as such, serve as the perfect material for William Caferro's new book, Petrarch's War, whose declared subject is “contradiction” and whose method, ultimately, is the subjection of received ideas and fashionable methods to interrogation in the face of the experience of rigorous and self-conscious archival research (p. 1). “Archives are subversive,” Caferro says, and this is, in many ways, a subversive book (p. 13). Resolutely revisionist and sometimes demandingly démodé—in an age of “big data” and global history and “usable” history—Caferro embraces the problematic and the anomalous, the short term and the small scale. Together with his impressive and prizewinning 2006 book, John Hawkwood: An English Mercenary in Fourteenth-Century Italy, Petrarch's War secures Caferro's place as one of the most important economic historians working today.