Civil Engineering Reference
In-Depth Information
h e Pan-
theon
As befits its imposing structure and astonishing state of preservation, the
Pantheon is a much discussed monument. However much of the discussion has
concerned issues which are now reckoned to be false tracks. In the i rst instance
the
rapprochement
of the classical ashlar prostyle porch with the concrete rotunda
raised persistent attempts to explain the monument as an agglomeration of several
periods of construction. h is is now known not to be the case and the monument
is the work of a single short period of construction, ca 120 AD-127 AD during
the rule of Hadrian. Secondly the concrete fabric of the rotunda was revealed to
contain a surprising inclusion of intricate brick arches and ribbing. Accordingly
there has been much speculation on the structural signii cance of this brickwork
but this has largely neglected the signii cance of this brickwork in constructional
procedure.
h e following brief discussion will touch on:
(1) h e ashlar porch and its adjustment to the rotunda with particular reference
to the giant Egyptian granite columns.
(2) h e inclusion of the brick arches and ribbing in the conrete fabric of the
rotunda.
(3) h e procedure for erecting the centering / shuttering for the dome of the
rotunda.
(1) h e ashlar prostyle porch
h e juxtapostion of the porch and the rotunda appears illogical, since the lines of
the porch do not accord in any way with the string courses on the rotunda which
are obviously designed to respond to them. h is indeed is so, but the explanation
is a relatively simple one. h e present design represents the best compromise
which could be made with an unfortunate mischance. h e porch was originally
designed to incorporate 50' granite column shat s, but it was found that column
shat s of this dimension could not be incorporated and substitutes of 40' were
incorporated instead. When this explanation was i rst recognised, it was assumed
that the reason why the designed 50 footers were not used is that they could not
be made available from the Egyptian quarries in time—a reasonable explanation.
However a later reconsideration proposes that shat s of this length could not be
raised up in the working space available, and thus had to be substituted by shorter
ones. h is came about through process of construction. According to this analysis
it is assumed that 20 granite shat s with a burden of over 50 tons would not be
erected by hoisting with block and tackle, but would be set up vertically using a
“rotating cradle” or “Adam tilter”. h is device for which there is no archaeologi-
cal evidence whatever was publicised by J.-P. Adam (
La Construction Romaine
,
p. 49, i g 98). h e defect is that a free linear space at least twice the length of the
96
97
