ROMAN URBAN TOPOGRAPHY in Britain and the western Empire

Fig 26 Stone wall construction using anathyrosis (rebating
to make unmortared edges fit tightly) and clamps
and dowels (Drawn by R Lea, after Coulton 1977,
fig 8)
experiences in carrying the Pergamene marbles down to
the coast at Dikili, a distance of only eleven miles, to
realize the enormous logistical problems faced by ancient
hauliers. To deal with larger blocks other methods had to
be devised-sledges, rollers, even the building of blocks
into huge wooden drums which could be drawn directly
by teams of oxen (Fig 23).
The next stage is the dressing of the masonry on the
actual building-site (Fig 24). Most of the preparation of
the blocks would inevitably be carried out here; one has
only to think of the ‘knapping floors’ excavated in the
vicinity of ancient masonry structures and to compare
modern practice as exemplified by the restoration work on
the Athenian Acropolis. The main task was to ensure that
contiguous surfaces would join tightly when the blocks
were bedded, or rather that the visible edges would join
tightly; the hidden parts would often be slightly hollowed.
Exposed faces, however, were frequently left rough in
order to receive a final working when the blocks were in
position, and there might also be projecting bosses to
facilitate lifting and levering during construction. Sometimes
these rough surfaces and projecting bosses still
survive because buildings were never completed; sometimes,
as in the Porta Maggiore and other architecture of
the emperor Claudius in Rome, they were deliberately
retained to produce the effect known as rustication. But in
all cases the outer margins of the visible face were chiselled
smooth to allow the use of a chalk-line and plumb-line to
check the horizontal and vertical during construction.
Once the masonry was dressed it had to be lifted into
position. Roman builders, like the Greeks before them,
were conversant with block-and-tackle systems, and
examples are illustrated in art of the imperial period, as on
a painting found in the Villa San Marco at Stabiae (Figs 24
and 25). This shows a small derrick operated by two
workmen turning a drum by hand, one half a turn ahead of
the other. That surprisingly simple contraptions could be
used to hoist quite heavy blocks is demonstrated again by
the modem equivalents operated by the restorers on the
Athenian Acropolis. Much more powerful and more
elaborate, however, were the cranes operated by treadwheels
which are represented on reliefs from the
21
Ling: The mechanics of the building trade
amphitheatre at Capua (Fig 25) and from the tomb of the
Haterii in Rome. The latter is depicted in association with
some of the major Flavian monuments erected in the
capital, such as the Arch of Titus and the Colosseum, and
there is little doubt that it is the kind of machine used by
the leading construction companies of the time. The
actual blocks lifted by such machines often bear the marks
of the means by which they were attached, including
wedge-shaped holes in the upper surface for a lewis. The
projecting bosses already mentioned were probably not
strong or large enough in themselves for lifting and were
intended rather to prevent ropes from slipping or to help
in the task of manoeuvring a block once it was more or less
in position. Small holes for levers testify to the same final
process of manipulation. How the builders managed in the
case of the largest blocks is a matter for speculation. In
Greek and Egyptian work the huge architraves of the great
stone temples were slid up purposely constructed ramps,
and something of the same sort may have happened in
Roman times too, as in the podium of the great temple of
Jupiter at Baalbek, some of whose blocks weighed almost
1000 tons.
Methods of fastening again followed the Greek tradition.
In normal coursed masonry holes for horizontal
cramps and vertical dowels would probably be cut across
joints after the blocks were in position (Fig 26); visible
examples of cramps (Fig 27) show a variety of shapes,
including the double T or H, the double swallow-tail, and
a straight bar with arms descending vertically at each end
(ie, seen in profile, a Greek letter ). The cramps were of
iron, or more rarely bronze, and, after they had been
inserted into the holes, were secured with an infusion of
molten lead. The treatment of column-drums was different,
because no fastening-device could be inserted after
the drums were in position; here carefully centred square
holes (chuck-holes) were cut in the upper and lower
surfaces and a wooden plug inserted before each drum was
lowered into position.
The final stages in the construction of an ashlar building
(apart from the roof, which is common to structures in
other media too) are those of adjustment and surface
dressing. The final dressing had to be carried out after the
blocks were in position, because a thin layer of stone had
hitherto been left to protect surfaces from damage during
Fig 27 Bronze clamp, set in lead in a dovetail socket,
joining two blocks of a door-sill; on Delos (Photo:
L A Ling)