buildings crowned by a large dome: namely, that such a dome, to
produce the greatest effect possible, should rise either from the
centre of a Greek cross, or from the centre of a structure of which
the plan has some symmetrical affinity to a circle, this circle
being at the same time the centre of the whole plan of the building.

Leonardo's sketches show that he was fully aware, as was to be
expected, of this truth. Few of them exhibit the form of a Latin
cross, and when this is met with, it generally gives evidence of the
determination to assign as prominent a part as possible to the dome
in the general effect of the building.

While it is evident, on the one hand, that the greater number of
these domes had no particular purpose, not being designed for
execution, on the other hand several reasons may be found for
Leonardo's perseverance in his studies of the subject.

Besides the theoretical interest of the question for Leonardo and
his_ Trattato _and besides the taste for domes prevailing at that
time, it seems likely that the intended erection of some building of
the first importance like the Duomos of Pavia and Como, the church
of Sta. Maria delle Grazie at Milan, and the construction of a Dome
or central Tower_ (Tiburio) _on the cathedral of Milan, may have
stimulated Leonardo to undertake a general and thorough
investigation of the subject; whilst Leonardo's intercourse with
Bramante for ten years or more, can hardly have remained without
influence in this matter. In fact now that some of this great
Architect's studies for S. Peter's at Rome have at last become
known, he must be considered henceforth as the greatest master of
Dome-Architecture that ever existed. His influence, direct or