However unsatisfactory the execution of the figures may be, the Confirmation
of the Rule and the St Francis preaching before Honorius III have the most organic
spatial constructions of all the Upper Church frescoes. These scenes, which
have a perfectly centralized view point, are two of the most outstanding examples
of Giotto's conception of space as a cubic box open at the front. Notice how
cleverly this space has been contrived. Our attention appears to be drawn to
the upper part of each fresco, occupied by a series of protruding arches supported
by sturdy consoles in the Confirmation of the Rule, and by the first surviving
depiction of a cross vault in the history of Italian painting in the St Francis
preacbing before Honorius III. Such perfection of spatial construction is found
only in the frescoes in the Arena Chapel, Padua, and the Bardi Chapel in Santa
Croce, and those in the right transept of the Lower Church at Assisi, all of
which are by Giotto. Another noteworthy feature of the Confirmation of the Rule
is the arrangement in depth of rows of kneeling friars behind St Francis. Duccio
preferred to arrange the saints in horizontal rows parallel to the picture plane
in his Maestą at Siena, while Simone Martini showed the rows of figures around
the Virgin at a slightly oblique angle in his Maestą in the Palazzo Pubblico,
Siena. The latter system had been introduced and systematically employed by
Giotto, in perfect harmony with his conception of pictorial space.