The windows are few and narrow, so that little light even at noonday struggles through them; and broad barren spaces of grey walls oppress the eye.

Externally the whole church is panelled with parti-coloured marbles, according to Florentine custom; but this panelling bears no relation to the structure: it is so much surface decoration possessing value chiefly for the colourist.

Arnolfo died before the dome, as he designed it, could be placed upon the octagon, and nothing is known for certain about the form he meant it to assume.

It seems, however, probable that he intended to adopt something similar to the dome of Chiaravalle, which ends, after a succession of narrowing octagons, in a slender conical pyramid.[23] Subordinate spires would then have been placed at each of the four angles where the nave and transepts intersect; and the whole external effect, for richness and variety, would have outrivalled that of any European building.

It is well known that the erection of the dome was finally entrusted to Brunelleschi in 1420.