This manuscript is an illustrated account of the events relating to the famous Battle of Montaperti of September 4, 1260, which is mentioned by Dante in TheDivine Comedy. The battle resulted in the victory of the armed faction of the Ghibellines, supporting the Holy Roman Emperor and led by Siena, over the Guelphs, supporting the pope and led by Florence. The manuscript was written and illustrated throughout by Niccolò di Giovanni di Francesco di Ventura da Siena, who signed it and stated that he completed the text on December 1, 1442, and the illustrations the following year. Little is known about Niccolò other than his name, which is first recorded in September 1402. He appeared on the list of the members of the painters' guild in 1428 and died on April 1, 1464. It is generally agreed that the text is the result of an elaboration of the myth of Montaperti, dating from at least a century earlier, and that it was copied from one or more previous accounts, perhaps with insertions of further facts and information gathered from secondary sources. The illustrations, still bearing 14th-century stylistic traits, also were in all likelihood reproduced from older models. In the absence of contemporary records of the battle, this very popular account represents a precious historical source, thanks to its apparent accuracy and to the richness of its illustrations. The manuscript belonged to the Carmelite prior general, Giovanni Battista Caffardi. It was transferred from its original location in the convent of San Niccolò in Siena to the Biblioteca comunale degli Intronati di Siena in the 18th century by command of Grand Duke of Tuscany Pietro Leopoldo.