This is a transcript of an episode of Public Address Science which was originally broadcast on Radio Live, 29th September 2007, 5 pm - 6 pm.
You can listen to the original audio version of the programme by clicking on the 'Play the audio for this post' link at the top of this page or the 'Audio' button at the bottom of this page.
Background:
[Sound of military drums and crowd chanting: "Caesar, Caesar, Caesar..."]
[Sound of wind over high-tension power lines]
Voiceover:
150 AD was a good year for the Roman Empire. In fact, arguably, things would never be better. The empire encircled the Mediterranean and stretched into Northern Europe as far as Britain. It touched the western edges of the European and African continents in what are now the countries of Portugal and Morocco, and it reached eastward into Asia as far as Azerbaijan. In the south it stretched into Africa to embrace the Red Sea and modern-day Sudan [1].
The Roman emperor in 150 AD bore the snappy name of Caesar Titus Aelius Hadrianus Antoninus Augustus Pius -- a man who Roman historians later described as the fourth of the five good Roman emperors -- and who (only two years previously) had presided over the celebrations for Rome's 900th anniversary [2].
Background:
[Sound of crowd chanting: "Caesar, Caesar, Caesar..."]
Voiceover:
And, unquestionably, one of the greatest jewels of the Roman Empire in its heyday -- and, certainly, its intellectual centre [3] -- was the city of Alexandria in what is now the country of Egypt.
Background:
[Sound of fire burning]
Voiceover:
In last week's episode, I talked about humankind's exploitation of the energy in plant biomass (via the process of burning), and how this enabled stone-age humans to make two paradigm shifts in development: firstly, to rise to the top of the food chain and spread out across the globe; and, secondly, to develop agriculture and harness additional energy in the form of animal labour. In the subsequent three-and-a-half thousand or so years between the first widespread use of animal labour, and the birth of the Roman Empire, the repercussions of energy from fire and animals unleashed a cascade of new
technologies. And the best place in the ancient world to learn all about these new technologies was the city of Alexandria in the Roman Empire.
Background:
[Sound of wind over high-tension power lines]
Voiceover:
The Mouseion in Alexandria [variously spelt Museion or Musaeum; from which we get the modern word 'museum'] was the empire's most famous scholarly institute [4]. It included the famous Library of Alexandria [5] -- and although this had probably been partially destroyed by 150 AD [6], it was still a vast repository of knowledge. Scholars at the Mouseion both archived and conducted research into history, literature, philosophy, science, and all forms of engineering.
Background:
[Egyptian street sounds]
Voiceover:
And if we were to walk out onto the streets of Alexandria as it was in 150 AD, we would see a city which -- from a technological perspective -- would appear (initially, at any rate) to be little different from a modern city of, say, three hundred years ago.
Alexandria is a clearly a city from the Age of Metals. The energy from fire has enabled the production of copper, bronze, wrought iron, and steel [7] -- and these materials are widely used in day-to-day living.
There are public baths with hot water, and even central heating [8]. Energy from animal labour is exploited to haul carts and wagons around the city. And in the harbour, sea-going vessels propelled by wind energy bob up-and-down in the waves.
Background:
[Sound of wind over high-tension power lines]
Voiceover:
And all of this has arisen from humankind's ability to exploit non-food forms of energy. Of course, there are clearly other factors involved as well. For example, metals can't exist without the appropriate ores being available, and agriculture can't exist without animal or plant species suitable for domestication. But, beyond that,
the single physical limiting factor is energy, and the technology to exploit it.
The cities of the Roman Empire, and the agricultural lands that supported them, and the Roman military forces, and the scale of the empire's trade and commerce on land and sea, simply would not have been possible -- and couldn't even have come into being -- without the exploitation of energy from fire, animal labour, and wind.
Background:
[Sound of horse and cart]
Voiceover:
Having noted the apparently advanced level of Roman technology, it therefore comes as a surprise when we take a closer look at the way they used their energy resources. For example, although they have greatly increased the load-carrying efficiency of horses by use of the wheel and axle (and the famous Roman roads), the harness system on Roman horses looks rather odd -- hardly more sophisticated than a dog-collar.
In fact, the Roman harness was extremely unsophisticated, and also extremely inefficient. It turns out that a horse with a late-medieval harness could haul about 15 times that of a human -- but a horse with a primitive Roman harness could only haul about four times that of a human [9]. And since a horse eats about four times as much as a human [9] then -- interestingly -- horse-power with an inefficient Roman harness only becomes sensible for applications that require speed rather than pure hauling ability.
Background:
[Egyptian street sounds]
Voiceover:
And that means that in the Roman Empire, human labour would very often be employed in situations where -- a thousand or so years later -- horses would have been used. Farms in the Roman period required a virtual army of labourers, many of whom would be simply lifting and carrying. The energy to run the construction cranes on Roman building
sites was derived from humans turning windlasses. And even the grain mills and water pumps were often powered by people running around inside machines that resembled enormous human-sized hamster wheels [10].
Background:
[Sound of waves and seabirds]
Voiceover:
And what about those Roman sailing ships bobbing about in the harbour? They're certainly a triumph of craftsmanship -- but a closer look at the sails reveals another surprise. The design is dramatically different from that which would be used in Europe a millennia later. The Roman ships used drag-type sails, which can only provide tractive force in the same direction as the wind [11]. If the captain wishes to sail against the wind, his only option is to lower the sails, and order his team of rowers to get to work.
So, although Alexandria in 150 AD initially appears to be technologically similar to cities of only two or three hundred years ago -- in its use of fire, animal labour, and wind energy -- in turns out that the major source of energy for useful work in the Roman Empire was, in fact, animal labour from other humans. In other words: slavery.
Background:
[Sound of military drums]
Voiceover:
First and foremost, Rome was always a military power. The Roman Republic existed in a state of continuous warfare and conquest [12]. Military victories resulted in the transfer of enormous material resources into Rome [13] -- and none was more important than slaves. Slaves (and other spoils of war) enabled the Romans both to consolidate their conquests, and also to embark on further expansion [12].
Vast numbers of slaves were used on the Roman agricultural estates. Slaves performed essential work in the factories of the Roman cities. Hordes of slaves rowers allowed Roman ships to travel against the wind. And slaves provided
the labour in the Roman metal-mining industry.
Background:
[Sound of wind over high-tension power lines]
Voiceover:
Historians estimate that in the first century of the empire, Rome consumed between one hundred thousand and half-a-million slaves every single year [14][15]. The slaves used for hard agricultural labour and as rowers in Roman ships had a life-expectancy of perhaps only a few years -- and those in the mines only a few months. Slaves were, quite simply, an energy resource to be exploited. Nevertheless, despite the high mortality rate, such was the quantity of slave imports that they comprised between 30 and 40 per cent of the population in the empire's Italian provinces -- an enormous proportion [14].
Background:
[Egyptian street sounds]
Voiceover:
Now the year 150 AD is particularly interesting in terms of slavery. Nine hundred years of continuous Roman growth and expansion has reached its peak under the Emperor Trajan in 116 AD [16]. In the subsequent decades, the supply of new slaves began to slow. Breeding programmes, piracy, poverty slavery, and child abandonment within the empire proved insufficient to make up the shortfall of new slaves -- and, around 150 AD, the demand for slaves began to exceed supply, and labour shortages began to seriously affect the empire [15].
Which provides an interesting lesson: what happens to a civilization when its main energy source begins to run out? At the very least, economic and political instability. But this need not be a mortal blow: for example, in the case of Rome, technological development in terms of a more efficient horse-harness or lift-type sails on Roman ships could, perhaps, have greatly reduced the empire's energy consumption for agriculture and transport.
And, of course, wind-power, waterwheels [17], and possibly even tide-wheels [18] were all known technologies that would have been documented
in the Library of Alexandria. But these required the right sort of rivers, the right sort of tidal location, or a reliable supply of wind. And besides, from the Roman perspective, slavery was clearly a winning formula -- after all, Rome had prospered for 900 years on the energy of its slaves.
Background:
[Sound of wind over high-tension power lines]
Voiceover:
Clearly, there were many contributory factors in the collapse of the Roman Empire. But I would argue that energy was a critical underlying cause -- often overlooked -- that ties together a number of other important factors. To put it in very simple terms, the importation of energy in the form of slaves allowed Rome to expand beyond an internally sustainable size. When the energy imports stopped -- then civilization collapsed back to its sustainable limits. The western empire fragmented into smaller regions, and the less energy-dependent east (which was more densely populated; had easier trade routes into Arabia, China, and India [19]; and was historically less dependent on slavery [15]) became the Byzantine empire.
Background:
[Sound of waves and seabirds]
Voiceover:
One of the themes of this series is that the exploitation of energy has allowed civilization to arise -- but the Roman empire may well provide a cautionary example that the reverse can also happen when energy resources are lost.
Next week, on a more cheerful note, we step forward in history to an obscure former part of the Roman Empire -- and onto the high seas...
- Read about the Roman Republic in Wikipedia.
- Read about the Roman Empire in Wikipedia.
- Read about the The Library of Alexandria in Wikipedia.