The section of a gallery given in the sketch to the right below
shows the roof to be constructed on the principle of superimposed
horizontal layers, projecting one beyond the other, and each
furnished with a sort of heel, which appears to be undercut, so as
to give the appearance of a beam from within. Granite alone would be
adequate to the dimensions here given to the key stone, as the
thickness of the layers can hardly be considered to be less than a
foot. In taking this as the basis of our calculation for the
dimensions of the whole construction, the width of the chamber would
be about 25 feet but, judging from the number of urns it
contains--and there is no reason to suppose that these urns were
larger than usual--it would seem to be no more than about 8 or 10
feet.

The construction of the vaults resembles those in the galleries of
some etruscan tumuli, for instance the Regulini Galeassi tomb at
Cervetri (lately discovered) and also that of the chamber and
passages of the pyramid of Cheops and of the treasury of Atreus at
Mycenae.

The upper cone displays not only analogies with the monuments
mentioned in the note, but also with Etruscan tumuli, such as the
Cocumella tomb at Vulci, and the Regulini Galeassi tomb_[Footnote 1:
_See_ FERSGUSON, _Handbook of Architecture, I,_ 291.]. _The whole
scheme is one of the most magnificent in the history of
Architecture.

It would be difficult to decide as to whether any monument he had
seen suggested this idea to Leonardo, but it is worth while to
enquire, if any monument, or group of monuments of an earlier date