The splendidly evocative ruins of Ancient Rome
have long been a challenge to historians and archaeologists
intent on reconstructing how that city once looked and functioned.
During the Imperial period, the city grew larger
than any before in the Western world.
How was the city constructed and what were the materials used?
How was it defended?
How was the population supplied with food and water?
How were the people housed and entertained?
Above all, how did the Romans make the city work?
This model shows how Rome might have looked
during the reign of the Emperor Constantine.
The population at its peak was probably a million,
enormous by ancient standards and five times that of Alexandria,
the next largest city in the Roman Empire.
Meeting even the basic needs of such a population,
let alone the construction of monumental public buildings,
surely required considerable engineering
and organisational ability.
Yet the Romans themselves have the reputation
of contributing nothing of note to the history of technology.
By this account they were completely uninventive.
All they did was appropriate the innovations
of the peoples they conquered.
How can we reconcile these two judgements?
The ancient history of Rome lasted some thousand years
from the time they were ruled by kings, through the Republican period
which lasted some four centuries,
and then into the Empire when Rome reached the height of its power.
It's necessary to consider these issues
in the context of Rome's physical development.
The geographical setting combines fertile land
with ready access to the sea by the means of the River Tiber.
Equally vital was high ground for defensive purposes,
the famous seven hills of Rome.
As the city expanded into the valleys,
the marshy ground between the hills
was drained by channelling an existing stream into the River Tiber.
This became Rome's main sewer, the Cloaca Maxima,
still in use nine centuries later during the reign of Constantine.
Indeed, it is still in use today
despite modern landfill on the banks of the Tiber.
The first stone defences were built in the early Republican era,
the so-called Servian Wall.
They were carefully constructed with a locally quarried material
called tufa, a softish, sedimentary volcanic ash.
Easy to quarry, it continued to be used in the Imperial period
even after concrete became the main building material.
Although we tend to think about Roman construction of the Imperial period
in terms of concrete,
there was in fact a viable alternative
which was very much used in the early Republican period.
This is the use of large squared blocks of tufa
as we have here.
The use of these large tufa blocks
continued for some particular functions,
usually large public buildings,
right into the middle of the 1st century and beyond.
Notice how fine the joints are between the stones.
This means that work has to take place both at the quarry and on site.
Whereas concrete requires far less skilled labour.
Stone was also used to replace wood for building bridges.
Stones arches were necessary to span the river
as in the Pons Cestius built during the late Republic
and then replaced in the Imperial period.
The facing material of the later bridge was travertine,
another local stone.
This bridge has been rebuilt several times
but it still serves its original function,
connecting the right bank of the river with the Tiber Island.
Another important masonry structure is the Porta Maggiore
built in the early Imperial period.
This monumental double arch is also constructed with travertine,
a kind of limestone from nearby Tivoli.
Travertine, a much harder material than tufa
but more difficult to quarry,
was used increasingly in early Imperial buildings.
Beneath the Porta Maggiore survives a portion of road.
Like all major roads in the vicinity of Rome it was paved with basalt,
a very durable, local volcanic rock.
Even in this, deep ruts were worn by the constant traffic
of wheeled carts.
