Civil Engineering Reference
In-Depth Information
h e Colosseum is a large oval building, its horizontal axes 188 m × 156 m and
the outer wall rising to a height of ca 50 m above external pavement level. h e
plan is formed by a succession of arcs struck from a number of centres rather
than a true ellipse and all internal subdivisions parallel this curvature. h e vertical
supports of the structure comprise piers at the external margin of the plan; pillars
linked radially below the middle third of the cavea plan; and slight radial walls
at the inner third of the cavea plan. h ese supports are all aligned radially, i.e. to
make straight lines radiating from the centres of curvature of the periphery. h ere
is virtually no continuous load bearing ring walls. h e radial disposition of the
supports gives a ground plan of the cavea consisting of 4 annular main corridors
(ambulatories), 2 at the outer margin and 2 at the inner third, together with a
series of radial passageways at the middle of the plan which house stairs. h ese
passageways (
vomitoria
) provide for the vertical circulation and for interconnection
between the annular corridors which af ord the basic horizontal circulation.
h e piers are interconnected in the annular sense by arches and all the corridors
and passageways are roofed by vaults (in the main simple barrel vaults). h e vault-
ing over the radial passageways housing stairs is ramped, ascending from a single
storey at the innermost to 4 stories at the outer margin. h is rooi ng provides the
seating for the ascending rows of marble seats. h e cavea l oor thus ascends at
an angle of ca 30° in the lower circles and ca 40° in the upper circles, and all the
space below this provides the manifold circulation necessary to get a full house of
40,000+ spectators into and away from their seats. Finally englobed in a deep pad
of site concrete there are also subterranean chambers and passageways serving the
(brutal) spectacles in the arena.
All comment has noted the importance of the Colosseum precisely for the light
it throws on Roman construction procedure; but without, in fact, transmitting this
light very much. Certainly the Colosseum is the one great Roman building to show
that Roman builders retained a mastery of Classical Greek ashlar building construc-
tion while developing the full potentiality of Roman Concrete construction.
So much for the design of the building. Now is to be considered its construction
which was intended to provide for an imposing appearance; structural stability;
and also for an accelerated building schedule (something like 5-7 years, an aston-
ishing feat). h e scheme adopted by the architect for the amphitheatre to achieve
this aim was to employ two basically dif erent building materials in conjunction:
meticulously dressed ashlar masonry and Roman Concrete. h e ashlar masonry
was to provide the imposing aspect and the structural strength of the load bear-
ing supports, while the Roman Concrete was to af ord rapid construction where
neither impressive aspect nor great load bearing capacity was required. In this way
the grandiose façade and outer annular corridors were entirely of limestone and
h e Col-
osseum
28
207, 399
399
