Every school thinks itself sufficiently honoured when it can produce two or three painters of the thirteenth century: the school of Siena is peculiarly rich in them, and these are recorded in the twenty-fifth letter _On the disciples of Guido_. As usual I shall omit the names of those least entitled to recollection. I will not affirm that all of them proceeded from the school of Guido; for in a city where the fine arts flourished so rapidly, masters unknown to us may have been produced. Much less will I ascribe artists of other cities to this school. In the manuscripts of Mancini, one Bonaventura da Lucca is mentioned, who is the Berlingieri already mentioned.[260] I neither assign him to Guido nor to Giunta. Who can tell whether Lucca had not also in those early times an original school, now unknown to us? Setting aside uncertain points therefore, we can only assert, that after the middle of the century, Siena abounded in painters, more, perhaps, than any other city of Italy; and the causes of this are as follows. The cathedral was begun several years before, in a style of magnificence suited to the lordly views of the citizens. It was not a work to be completed in a short time: hence it was frequently interrupted, and a long period had elapsed before it was finished. During this time many architects (_magistri lapidum_) and sculptors either were invited from other places, or were reared up in the city; and in 1250 they formed a corporate body, and required particular laws.[261] Although nothing is ascertained with regard to their mode of study, it is natural to suppose that the study of sculpture contributed to the advancement of painting, a sister art. The celebrated battle of Monte Aperto, in which the people of Siena defeated the Florentines, happened in 1260. This victory produced an era of peace and opulence to the city, and encouraged both in public and in private the arts depending on luxury. The victory was ascribed to the interference of the blessed Virgin Mary, to whom the city was consecrated; the adoration of her votaries increased, and her images were multiplied in the streets, and in all other places; and thence painting obtained fresh encouragement, and new followers.