VIEW IN THE UPPER PART.
Details.
A A. Piers of the great corridor.
a a. Aperture from which a pier of travertine has been removed for building material, by the Barberini (?).
b b. Wall of brick, with arch of construction standing equally well without the support of the travertine pier.
c c. Wall of tufa, of a lower storey.
d d. Vault of a third storey, below.
e e. Remains of the vault of the stairs to the upper storey.
f f. Floor of the second corridor.
g g. Floor of the principal gallery.
The object of this plate is to make it still more clear that the brick arches of construction did not really rest on the piers of travertine, although at first sight they appear to do so. The Roman bricks of the first century are two feet square and one inch thick, but in these arches they are cut down from two feet to three or four inches at the impost, or springing of each arch, just where the greatest strength would have been required. They have evidently been cut through to admit the stone piers, which were required to carry the upper gallery, when that was built of stone instead of wood.