"And so successful was Spinello with his horrible and portentous Production that it was commonly reported—so great is alway the force of fancy—that the said figure (of Lucifer trodden underfoot by St. Michael in the Altar-piece of the Church of St. Agnolo at Arezzo) painted by him had appeared to the artist in a dream, and asked him in what place he had beheld him under so brutish a form."
Lives of the most Excellent Painters, by Giorgio Vasari.—"Life of Spinello."