James J. Walsh, The century of Columbus
“ The Umbrian School of painters includes a group of men born in the hill towns of Umbria, to be credited, therefore, to more than a single city, but their greatness is sufficient for the glory of any number of cities,--Gentile da Fabriano, Bonfigli, Perugino and his pupils, Pinturicchio, Lo Spagna, and many others, above all Raphael. ”
