Vasari boldly ascribes the whole upper portion of the church to Cimabue, and the lower to Giotto: Lindsay asserts that Giunta Pisano had painted the upper, Cimabue the middle, and Giotto the lower range of compartments: Kugler, though somewhat indefinite, holds that he worked out his apprenticeship in the Upper Church of Assisi, and afterwards came again and laboured in the Lower one.
To sum up then the discussion of this matter, which is hardly an interesting one to the general reader, my explanation of the probable authorship of the lower row of frescoes would be the following. That they have been painted by a pupil of Giotto's at the same time that the master himself was at work on the frescoes in the Lower Church, and that the only frescoes by Giotto in the Upper Church, are the two almost monochrome compositions that are placed one on each side of the principal entrance. It should be noted that these two are far more conspicuous, owing to their isolated position, than any other frescoes in the church, which may well have been the reason for their execution by the master himself. And it is somewhat curious to observe that they are both painted in little more than two shades of colour, and are the only frescoes in the church so painted, as if Giotto were purposely restraining his hand, so as not to spoil by contrast the cruder work of his pupil. This pupil I believe to have been Taddeo Gaddi; but I have not seen sufficient undoubted works by his hand, to render this more than a mere conjecture, and there is no evidence on the subject whatever, save such as may be inferred from the fact that Gaddi was almost certainly present with Giotto at the time he painted in the Lower Church.
Leaving the question of the actual authorship undecided just now, notice how far this hypothesis, besides having strong internal evidence in its favour, goes to solve the difficulties of this matter; by it we account easily and naturally for the Giottesque qualities which we find in these works, and also for their comparative feeble significance. And by the effort to combine the Byzantine manner of Cimabue with the simplicity of Giotto, we account for all the very inferior architecture with which these pictures are crowded: architecture which is to a certain extent Giottesque in form, but seems to be wholly conventional in colouring and arrangement.