peculiarities, such as the odd egg and dart moulding which reappears
on the Annunciation. The colour effects are obtained by porphyry and
inlaid marbles. But we see how much Donatello trusted to sculpture,
and how indifferently he fared without it. This gallery does not
retain one's attention. There is a stiffness about it, almost a
monotony, and it looks more like the fragment of a balcony than a
_Cantoria_, for there is no marked terminal motive to complete and
enclose it at either end. Two gateways have been ascribed to
Donatello, but there is nothing either in their architecture or the
treatment of their heraldic decoration, which is distinctive of the
sculptor.[82] There can be no doubt that Donatello was employed as
architect by the Chapter of Sant' Antonio at Padua,[83] and his love
of buildings is constantly shown in the background of his reliefs. But
the strongest testimony to his architectural skill is derived from the
fact that he was commissioned in 1416 to make a model for the then
unfinished cupola of the Cathedral at Florence. Brunellesco and Nanni
di Banco also received similar orders. Brunellesco alone understood
the immense difficulty of the task, and in the next year he announced
his return to Rome for further research. In 1418 the sum of two
hundred gold florins was offered for the best model, and in 1419
Ghiberti, Nanni di Banco, Donatello and Brunellesco all received
payments for models. Donatello's was made of brick. Ultimately the
work was entrusted to Brunellesco, who overcame the ignorance and
intrigues which he encountered from all sides, his two staunch friends
being Donatello and Luca della Robbia. As to the nature of Donatello's
models we know nothing; it is, however, clear that his opinion was at
one time considered among the best available on a problem which
required knowledge of engineering. As a military engineer Donatello
was a failure. He was sent in 1429 with other artists to construct a
huge dam outside the besieged town of Lucca, in order to flood or