In Vasari 's Florentine version of art history, painters - according to the beginning of the Life of Giotto - owe a debt to nature and to Giotto. To nature the debt is owed because it serves painters as an 'example so that they may select her best and most beautiful parts for reproduction and imitation'; to Giotto the debt is owed because when the methods and outlines of good painting had been buried by many years of war he revived it to 'a condition which might almost be called good'. He became such a good imitator of nature that he abandoned the 'crude Byzantine style' ( Vasari, Le Vite, Testo II.95). He had a high reputation for the excellence of his figures, for his order, proportion, and truth to nature ( Vasari, Le Vite, Testo II.100). His works are 'truly marvellous when compared with those of the masters who preceded him' and he 'did extremely well for his day'( Vasari, Le Vite, Testo II.120). However he agreed with Dante that Giotto's work was superseded by later painters.
Dante ( Purgatorio, XI, 4-6) explained this in terms of the fickleness of fame; for Vasari it was a mark of progress. Giotto was good for his time, but he was only an early part of a process which would lead to Michelangelo. Early painters, even Giotto, did not deserve glory when judges by the 'perfect rule of art' achieved in the third and final phase of the development of art ( Vasari, Le Vite, Testo III.13; Preface to Part Two of the Lives).
Ruskin shows some traces in Modern Painters I of Vasari's approach, but Ruskin went on to develop a much more sympathetic understanding of the Byzantine schools of art and architecture, and he valued Giotto, not as the beginning of a process, but as someone who had made the most perfect works (see Ruskin on Giotto).