What is the core reason for our current dramatic increase in prosperity (seen as the Industrial Revolution, since 1750/1800)? The usage of new energy sources like coal and oil, to replace the physical labor of humans and animals with machines that dramatically boost our productive capacity. 

Could the same have happened to our Roman ancestors? Are their technologies linked to energy usage? Let's look at some distinct Roman practices that largely disappeared after the fall of Rome and see if they're linked to the usage of large amounts of energy. 

Baths

The Romans were renowned for their elobarate bathhouses. They contained large, heated water basins. The heating process required significant amounts of fuel. They seem to have fell out of use in the Medieval Period. Large spas reappeared in Europe during the end of the 18th century - at the start of the Industrial Revolution. 

Concrete

It was known before Rome, but Romans improved the recipe and used it extensively. Descriptions mostly focus on the ingredients and not the fuel usage. The Romans seem to have used a mixture of quicklime, pozzolana and pumice. It has been suggested that this knowledge was lost, explaining why their Medieval descendants barely used concrete. But let's go back to Wikipedia:

After the Roman Empire, the use of burned lime and pozzolana was greatly reduced. Low kiln temperatures in the burning of lime, lack of pozzolana, and poor mixing all contributed to a decline in the quality of concrete and mortar.

Apparently, the Romans used high kiln temperatures and their descendants struggled to reach these temperatures. After many centuries where only small amounts of low-quality concrete were used, concrete reappeared as a major construction material during the... Industrial Revolution! What a coincedence. Portland cement was patented in 1824, and reinforced concrete was invented in 1849. And once again, Wikipedia:

Portland cement clinker is made by heating, in a cement kiln, a mixture of raw materials to a calcining temperature of above 600 °C (1,112 °F) and then a fusion temperature, which is about 1,450 °C (2,640 °F)

Producing concrete seems to require very high temperatures!

Armor 

Rome was famous for its military strength. On the left, we see the equipment of the famous Roman legionaries, implemented during the Marian reforms in 107BC. These legionaries were not the Roman soldiers who lost the battles of 476AD. By then, they had been replaced by the comitatenses on the right. I'm not an expert in the precise requirements of crafting armor, but the plate armor worn by the legionaries seems like it should have required more iron and more smithing work than the chainmail worn by the comitatenses. In general, the equipment of the comitatenses seems 'cheaper', more primitive. They start looking a little... medieval. I wish I could say legionary-style armor was adopted again during the Industrial Revolution, but alas. (Although...)

Bricks

Before the first century AD, the Romans used mudbricks. They were dried only in the sun, which made them relatively weak and only suited for small buildings. Then they learned to dry their bricks in kilns, which resulted in stronger bricks and a boom in building projects. But when the Medieval Period starts...

After the Western Roman Empire fell in the 5th century many of the commercial stone quarries in Europe were abandoned. This led to a consistent pattern of reuse of Roman building materials throughout the next several hundred years. Like much of the Roman stone, Roman bricks were gathered for reuse throughout this period.

(Source)

And guess when bricks came back?

Production of bricks increased massively with the onset of the Industrial Revolution and the rise in factory building in England.

(Source)

Others

This list could be extended. The same pattern repeats for many products and habits. Roof tiles as compared to straw roofs, ceramic amphorae compared to wooden barrels, cremation compared to burial, the use of glass, even the toga seems to have required extensively boiled wool. They peak somewhere around the first century, decline or nearly disappear towards and during the Medieval Period, and if they come back, they do so during the Industrial Revolution.

I've read a lot of separate explanations for these trends. The recipe for concrete was lost. Bathhouses just fell out of fashion. Christianity prohibited cremation. They lost the know-how required to make proper earthenware. 

I don't buy it. All of these practices share one common ingredient: the need for significant amounts of fuel. If fuel steadily became more expensive throughout the centuries, that would explain why people gradually switched to more affordable alternatives. 

Roman Peak Oil?!

The Romans were not or barely using finite fossil fuels like coal, oil and natural gas. They relied on firewood and charcoal - which is made from wood. These are renewable resources. How did they manage to turn a renewable resource like wood from abundant and cheap to scarce and expensive? 

That can only be explained by a growing population that puts a lot of pressure on land. Farmlands would have displaced forests - even when forests were desparately needed to keep enjoying old luxuries like bathhouses, bricks and roof tiles. 

But that does not fit the history books. These claim that the fall of Rome was a tragedy which resulted in a serious population decline, which took many centuries to recover. During the Early Middle Ages, Europe was a depopulated continent, where sparse population centers were separated by regrowing forests filled with bandits. 

After population decline following the disintegration of the western half of the Roman state in the fifth and sixth centuries, Europe probably re-attained Roman-era population totals in the twelfth and thirteenth centuries and, following another decline associated with the Black Death, consistently exceeded them after the mid-15th century.

(Source)

Conclusion

So, we found a neat theory that clearly explains why famous Roman practices and luxuries gradually and simultaneously disappeared, not to return until the Industrial Revolution and new access to plentiful energy. But this would require scarce firewood/charcoal, which would require scarce forests, which would require scarce land, which would require a growing/large population - while everybody believes that the Early Middle Ages had a declining/small population. We'll have to investigate population pressure! I'll write about that in the next blog. 

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