Roman concrete is a fascinating subject and the uses Rome made of
concrete may surprise modern people. Some may also be surprised to
learn there are 2000 year old Roman concrete structures still in daily
use. The formula for making concrete has been known since the time of
ancient Egypt and Mesopotamia.
The Romans did make one change which allowed their concrete to last
through the centuries in spite of weathering . Their addition was
"pozzolana." Pozzolana is a fine grained volcanic sand which is very
hard and can resist wear and abrasion better than the soft lime which
bound the pieces of gravel together in regular concrete made only of
lime, sand and gravel. Today, modern cement manufacturers use silica
from blast furnace slag to replace the pozzolana used by the Romans
when making "Portland" cement used in construction.
Since I do not know how much you already know about Roman concrete, I
thought a little general background information may be of use.
Greek buildings are often described as constructed according to the
post-and-lintel system (i.e. mostly verticals and horizontals). We
can see the results in a building like the Parthenon, which is
constructed in great part of verticals (e.g. columns) and horizontals
(e.g. the architrave). However, when you ask - "what is new in terms
of the uses and purposes found for concrete construction techniques
(opus caementicium) for plans and elevations/facades?" -There was a
literal "concrete revolution" in architectural forms and design. In
Nero's Golden House you will find vaults and domes which were not a
part of traditional post-and-lintel construction. Here is an image of
Domus Aurea ("Golden House of Nero"): Octagonal room (plan and photo)
which shows how things changed. -
And another image of a vaulted ceiling from the same structure: -
Golden House (Domus Aurea) of Nero, the Room of Hektor and Andromache
The use of concrete allowed for a "plasticity" missing from more
traditional construction methods. As for the use of opus
caementicium, it was the normal construction technique used in villas
of the late Republican and early Imperial periods. Often walls made
in opus caementicium are covered with other materials to make a more
artistic and workable surface. These techniques are called opus
incertum, opus reticulatum, opus latericium and opus mixtum and were
largely reserved for public buildings.
The use of concrete also changed the way many building facades were
designed. Weight bearing columns were often replaced with decorative
columns and pilasters since the concrete itself carried the building
A good example of columns (or the appearance of columns) in a
decorative role rather than being support structures is found in the
Porta Maggiore - http://www.nycerome.com/rome-hotels-images/areas-of-rome-images/laterano-area-pictures/porta-maggiore.jpg
- where pilasters flank the arches. It carries two aqueducts, the
Aqua Claudia and Aqua Novus, over two major roads (Via Labicana and
Via Praenestina. Piggybacking two conduits over one another is
clever, and makes good engineering sense. The gate which is
reminiscent of a triumphal arch, is simply a special, architectural,
treatment of a stretch of these two aqueducts.
The use of concrete created a whole new "canvas" of building facades.
Design was no longer restricted to the weight supporting elements of a
building's face and could be turned more into decorative items.
As for Villa Jovis, emperor Tiberius' retreat eastern end of the
island of Capri, it was virtually designed around a courtyard
supported by a vast network of concrete, vaulted cisterns. Although
not designed to be viewed as such, it would have been a dramatic space
to see. The construction of such cisterns could not have been possible
without advanced concrete technology. This type of underground
supporting structure also opened up the architects 'creativity' as a
buildings foundations and plans became less dependent on natural
The Romans also knew that concrete had to be reinforced. They did not
have the steel rebar we do today so they used ropes of vitreous china
They also did not "pour" concrete as we do. They "tamped" it into
place. Using texts from the original Roman authors and the few
pictures we have of their construction methods, Romans mixed the
cement mortar for their concrete like they would mortar for bricks -
in a mortar box with a special hoe. A key element of the process is
that they kept the moisture content low, so that the mortar was
thicker than we are used to, resulting, in essence, in what we would
call a "no slump" mixture. The Romans couldn't have "poured" their
concrete even if they wanted to - it was too thick.
They then hauled the mortar to the wall in baskets. They laid down a
layer of rocks (aggregate) by hand, and then pounded the mortar into
the rocks using a special tool called a "beetle" to get all the air
out and make close compaction with aggregate and the layer below. So,
the Romans did not mix or pour concrete the way we do, they in
essence, mixed the mortar and aggregate (resulting in concrete) right
in the forms themselves. This type of construction also allowed for
"changes in plan" at the last minute, something rather unthinkable if
the material were carved stone.
The two elements of this process, low water content and close
compaction, were part of the reason why Roman concrete has lasted so
long, in comparison with our concrete which sometimes doesn't last
more than a few years without cracking.
There is also the following to consider when discussing Roman concrete
and the change in building facades and plans. Roman concrete had some
very definite technical and practical advantages over the traditional,
and mainly Greek, methods of enclosing space by the use of cut-stone
and post-and-beam structures. The advantages of opus caementicium can
be summarized thusly - it was exceptionally strong and could span
great distances when shaped into arches, vaults and domes - it had
greater flexibility in molding space since concrete was virtually
"tamped" (or layered) into a formwork and took the shape of its
container - concrete is that sense is a "plastic" material - it did
not requite special, skilled labor, therefore, it was cheaper - it was
much faster to construct than laboriously cut ashlar masonry - since
concrete-vaulted roofing was fireproof, unlike the wooden-beamed roofs
of traditional systems, it was safer.
As you can see, the question you asked can have a vast response.
Minute changes here and there as well as the major ones of opening up
creativity and allowing for more plastic design.
search - Google
Terms - roman concrete - plus some slight knowledge as an archaeologist.
The following were used to compose the answer:
http://ancienthistory.about.com/library/bl/uc_geary_bas.htm - "Ancient
Buildings made of Artificial Stone" - From About.com
- You will find three photos from Sperlonga. - from University of
http://id-archserve.ucsb.edu/arthistory/152k/water.html - "Water
Supply Systems: Cisterns, Reservoirs, Aquaducts" - From UCSB
http://id-archserve.ucsb.edu/arthistory/152k/concrete.html - "Roman
Concrete" - From UCSB
http://ciks.cbt.nist.gov/~garbocz/appendix1/node4.html - "The history
and importance of concrete" - From Virtual Cement and Concrete Testing
If I may clarify anything before rating the answer, please ask.
Clarification of Answer by
25 Jul 2004 15:47 PDT
As for the Golden House, some of the uses of concrete had an effect on
future architecture in ways other than the simple use of concrete
itself. One of these was the first construction of a concrete dome
'for a private residence' rather than for a temple of the gods. The
architects designed two of the principal dining rooms to flank an
octagonal court, surmounted by a dome with a giant central oculus to
let in light. The 'private residence' is emphasized for the reason
such a dome being the 'first' in a private residence is a
"probability" rather than a fact set in stone. Future research and
excavation may yet uncover a previous use for the dome in private
residences. Any of these things we consider as "firsts" in Nero's
palace may have been predated by other similar work and we just have
not found it yet.
However, in spite of the fact there may be as yet undiscovered
precedent, Nero's contribution to Roman architectural style and theory
was emormous. It is the building of the Golden House which truly
marked the change between Greek post-and-lintal to the Roman tradition
of vaulted architecture in concrete. Before Nero, concrete was
thought to be simply utliltarian in nature for foundations, bridges,
aquaducts, etc. Romans already had the technical mastry of concrete
but had not thought of it as the "stuff of fine art." Nero changed
all of that.
Nero and his architects realized that the use of concrete could change
the way they approached design. It allowed them a vision based on the
interior void rather than the exterior solid.
I did not use the term "concrete revolution" lightly and it seems you
caught it and I am glad you did. Though I applied it to all of Roman
concrete rather than just the Golden House. However, we could say
that the Golden House was the real heart of the revolution.
In fact, the Golden House was 'nothing short' of revolutionary.
Earlier post-and-lintal construction was viewed in terms of the solids
- the walls, the columns, etc and the challenge was to arrange them in
as much harmony as possible.
Roman concrete vaulted architecture is similar when it comes to trying
to arrange things in harmony - but the basic forms taken into account
are not the solids but the voids between them.
Nero's architects arranged a harmony of simple shapes such as
rectangles, triangles, octagons, etc, and erected the concrete walls
on the periphery. If you look at the "octogon suite" you see a simple
shape. But the walls around it are very strangely shapped. In
architectural terms, the word "spandrel" is used to describe the space
left over between two designed solid features. In the House of Gold's
architecture, the masons actually built the spandrels, something
virtually unheard of before Nero. This inversion of the architects
vision "is" the concrete revolution of the Golden House.
The actual concrete technology used in the Golden House was not new
nor was it revolutionary. The revolution was in the artistic manner
of how the material could be used. The change from visualizing solids
into one of visualizing voids.
As for Sperlonga, it was a coastal property of Tiberius located south
of Rome. It was evidently his even before he became emperor and is
more representative of personal tastes of late republican nobility
rather than Imperial exuberance. The villa was constructed to
accompany a natural cave which was then landscaped as a showplace
setting for sculpture. The grotto once collapsed, nearly killing
What we do know is still very little. The villa itself has yet to be
fully excavated though we know it was enormous. The cave or grotto
had been turned into a nymphaeum, a setting for fountains and
The architectural components of the grotto include an outer rectangle
containing a triclinium and a fish pond. There was also an inner
circle which was the sculpture grotto which had glass wall mosaics and
colossal sculptural groups set within basins and cave niches.
Just in case you have a curiosity about the sculpture, though it has
nothing to do with the answer, the known pieces were the "Binding of
Polyphemus," "Scylla," and "the Destruction of Odysseus' Ship." There
were signed pieces by Rhodian artists.(Agesandrus, Atenadorus, and
Polidorus) Pliny namnes the same individuals as sculptors of the
Laokoon for recent survey of evidence, see B. Ridgway, Laokoon and the
Foundations of Rome," Journal of Roman Archaeology 2 (1989) 171-181. -
- You can see photos of the reconstructed sculpture here:
http://www.ips.it/turismo/spe_ve_e.html - The National Archaeological
Museum of Sperlonga
Of course the concrete construction at Sperlonga may have 'presaged'
some of the ideas found in the Golden House but there was no truly
revolutionary change at Sperlonga.
Of course by making such a statement, I'm sure to come across some
dramatic bit of concrete architecture associated with Sperlonga. In
order to avoid that, I am going to make my response to your
clarification request in two parts.
This one now - and the second after I have had some time to
investigate Sperlonga a little more fully. There must be something
there or you would not have asked. Give me a couple of days.
In the meantime, if you have need of further clarification, you know
where the button is and I look forward to it.
Clarification of Answer by
25 Jul 2004 23:42 PDT
The easiest explanation would be that an architect can think more
about designing the "space" being enclosed than about designing the
With the old post-and-lintel system, space or the "void" was enslaved
to the need for support structures such as columns and cross beams. A
large structure could be built in that manner but the interior would
have been a forest of columns needed to support a roof. The open
space between was restricted to what the strength of the crossbeams
would carry. So the "void" - the space - was secondary in the design
to the solidity of the support structure.
With the evolution of vaulted concrete architecture, the interior
space could 'open up.' Much wider areas could be spanned without
support structures. Great halls could be built with unobstructed
views from end to end without columns or other support structures
blocking the way. Large rooms could be created without central
support. Architects began looking at the 'space' they could create
and rather than putting up a structure where the interior space was
that which was left by "accident" after all the needed weight bearing
solid elements were in place, They could now design the 'space' and
erect the needed support on the periphery.
That does not mean a lot of impressive work could not be done on a
building's exterior. It still was. It means that the interior spaces
now became as important in making whatever impression was wanted or
needed as the exterior approaches were in the past.
Prior to the "concrete revolution" a building's exterior was the most
prominent place to create "design to impress." The interior rooms,
regardless of how luxurious the furnishings, were were still no more
than "accidents of design" restricted by the need for columns and
After the concrete revolution, a buildings inner space was no longer
an "accident of design." subject to the support structures. Now the
inner space itself could be designed and architects of the Golden
House took full advantage of that.
Therefore - 'a vision based on the interior voids rather than the exterior solids'
Since I'm an archaeologist, perhaps my terminology is at fault. I
guess architects may think of building interiors as "space" or simply
"rooms." I really don't know their terminology. But as an
archaeologist, I'm in the habit of speaking of interior space as
"voids." I shall try to avoid that if it will make things clearer.
I still working on Sperlonga seeing what I can find online. I have
also sent email to the Sperlonga Archaeological Museum. But if they
get the amount of spam the rest of us do, they might well dump it.
So, if I don't hear back from them in a day or so, I will use snail
mail. I hope somebody there reads English. My Italian is limited to
words such as "spaghetti" and "pizza."