Pliny the Elder’s 37 volume Naturalis Historia is the largest single work to have survived from the Roman Empire. It includes a description of the importance of Roman cement’s property of setting under water, especially useful for building ports.

“As soon as it is in contact with the waves of the sea and is submerged, it becomes a single stone, impregnable to the waves, and every day stronger”, he wrote.”

Here’s a bit more background on one of our most popular but these days highly emissions-producing building materials. 

From his vantage point on the western headland, the younger Pliny watched a strange cloud rising swiftly from the hills across the Bay of Naples thirty kilometres away. There had been increasing earth tremors for days, nothing especially unusual in Campania, but getting worse.

Pliny was 17. His uncle and adoptive father, Pliny the Elder, had ordered a galley to take him across the bay so he could examine the phenomenon and rescue relatives if necessary.

Pliny the Younger saw the cloud becoming an enormous vertical column, white with black dots tumbling upwards to a great height like an enormous tree trunk surmounted by branches spreading outwards across the sky. Glowing rocks were falling onto land and sea and coming closer. Broad flames shot out of Mount Vesuvius.

That night, the Elder Pliny had not returned. The upheavals were now so bad that Pliny’s villa was tottering, and the family decided to leave. Crowds of people were crushed together and panicking.

As the younger Pliny wrote later:

The carriages we had ordered were lurching to and fro, and we could not keep them still even when we wedged the wheels behind with stones. We looked back and saw the sea sucked away by the convulsive motion of the earth. Torn by gushing flames and zigzag flashes, the black cloud advanced over the land behind us like a flood. We covered our heads with pillows as a heavy fall of volcanic ash rained down on us, and everything was covered deep in the ash as if with snow. 

Pliny the Elder died on the further shore of a heart attack or the toxic gases in 79 AD. He had been in command of Rome’s western fleet at its base at Misenum in the Gulf of Naples. He was also an encyclopedist.

His 37 volume Naturalis Historia is the largest single work to have survived from the Roman Empire. In it, he describes the importance of Roman cement’s property of setting under water, especially useful for building ports.

“As soon as it is in contact with the waves of the sea and is submerged, it becomes a single stone, impregnable to the waves, and every day stronger”, he wrote.

What gave Roman concrete this property was one constituent, volcanic ash. Their hydraulic (underwater) concrete was to become a powerful strategic resource, supplied by the plentiful volcanic ash around the Bay of Naples. 

Rome’s navy and legions were responsible for exploiting the volcanic ash. Their Misenum naval base was adjacent to the port of Pozzuoli, which gave its name to the volcanic ash it exported – “Pozzolana”. Merchant ships carried it around the Mediterraneum wherever Rome was constructing strategic ports and buildings.

The next big seaport

A century earlier, Herod the Great was King of Judea (now part of Israel). Herod was a personal friend of the Roman Emperor Augustus, and both men had grand plans to increase trade between their lands and India, Sri Lanka and the Silk Road to China.

To do this, Herod wanted a great seaport to rival Egypt’s Alexandria. The problem was that Judea’s coastline of straight sandy beaches and a strong shoreline current made for poor anchorage. But Herod knew about Rome’s engineers and their pozzolana. And the friendly Emperor Augustus was only too happy to have his ships and legionnaires lend Herod a hand. 

To build a concrete harbour, pozzolana could be shipped from Pozzuoli to Judea. Another essential constituent was limestone, to be fired in kilns to produce lime. For this, a vast amount of wood for fuel would be imported from Lebanon and Syria. Mixing the volcanic ash with the lime, and with water added, produces a hot “pozzolanic” chemical reaction, binding sand and rubble to make concrete.

Still more timber was needed to make the formwork for moulding the concrete structures in the sea. The formwork would be floated into position, then sunk under the weight of the concrete. The result: two great encircling piers of 500 and 255 meters, sheltering an outer and an inner harbour. Sluices in the piers would direct a flow of the fast current into the harbour to sweep away siltation.   

It took eight years to build. Herod named the port Sebastos, meaning “Augustus” in Greek. On land, Herod built his palace and a new town, Caesarea Maritima. The promised trade prospered. Rome’s legions, and with them effective Roman rule, moved from Jerusalem to Caesarea.

A challenge to Herod’s ambition loomed – another, more southerly trade route. Caesar Augustus had annexed Egypt in 30 BC, which now became Rome’s portal for the growing trade through the Red Sea to India and beyond. Romans acquired a taste for oriental merchandise: fine materials, precious stones, ivory, pepper, slaves, wild animals, and rice, which was used as medicine.

Port Sebastos was no match for this, and another, unforeseen problem lay in the future. The massive harbour was built on a geological fault line running close to the coast. The piers were sinking, and in time they went five meters underwater.                            

The concrete revolution

Not so Rome, which was growing in capacity and wealth. That, and Roman concrete, enabled a concrete revolution in architecture. Magnificent buildings arose with curved shapes, complex arches, vaults and domes.

The Colosseum is built of stone and cement, erected on massive concrete foundations. It has 80 entrances leading to barrel-vault arcades and what were once marble seats for 50,000 spectators. For the opening ceremony, the arena was flooded for a mock naval battle between rival “armies” manning flat-bottomed galleys. Overhead, a huge retractable awning operated by hundreds of sailors protected the spectators from the sun.

The Pantheon, still today the largest unreinforced dome in the world, remains unblemished as it was when built almost two thousand years ago.

Records of technical knowledge that made the building possible did not survive the fall of Rome. Fortunately, an account of Rome’s architecture survived – the ten volumes of De Architectura written by Vitruvius. In it, he describes the extraordinary richness of Roman building design, engineering and mechanical methods. 

The De Achitectura manuscripts and other ancient Roman works that we have today were saved in Christian monastic libraries for hundreds of years. By the time of Charlemagne’s Frankish Kingdom (768 to 814), the Roman manuscripts were decaying and fragmented. Charlemagne established monastic scriptoria where monks made copies of the ancient texts, using Charlemagne’s new font – Italics. But there were problems. The scribes botched technical words and place names, and Emperor Charlemagne was often away from his court in Aachen, at war.

The newly copied manuscripts survived for several hundred years, though not much read.  

In Germany in the 1450s, Gutenberg invented the printing press with movable type. Printing presses quickly spread across Europe, leading to the mass production of books, greatly reducing their cost and increasing availability. The result: a cultural and information revolution that refocused the Middle Ages back to Classical Greece and Rome. Three editions of Vitruvius’ De Architectura were soon in print.

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Born in Verona, Friar Giovanni Giocondo was a teacher of Latin and Greek, a hydraulic engineer, architect, archaeologist of ancient buildings, and a translator and publisher of Classical Roman texts – a true Renaissance man of intellect and action. In Venice, he diverted the River Brenta to save Venice from flooding, a critical problem with the buildings being on low islands in a lagoon. Below water level, the foundations were wooden piles driven into the sand.

In 1489, Fra Giocondo was summoned to Naples to advise on fortifications. As an engineer and a classics scholar, Fra Giocondo would have studied the many ancient Roman buildings in nearby Pozzuoli, especially the Port Julius breakwater, constructed by Roman Empire forces to shelter its ships.

The breakwater was a line of 25 massive piers planted in the sea and joined by arches, not surprisingly made of the local pozzolana concrete. Fifteen centuries later, it must have appealed to Friar Giocondo’s ideas on hydraulic engineering.

In 1495, the friar went to Paris as a royal adviser and architect of Renaissance palaces. When the city’s old wooden bridge over the Seine collapsed in 1499, as many bridges there had done since before Roman rule, it was decided to build a new bridge of six arches and piers in stone, “Pont Notre-Dame”.

Fra Giocondo was chosen as architect. His design of the foundations would be critical because the riverbed was muddy and soft deep down.   

For advice Fra Giocondo looked back fifteen centuries to the words of Vitruvius, who replied: “If the site is soft it should be reinforced with pilings [which] should be driven into place by machinery, as densely packed as possible …Alderwood when densely fixed as pilings under foundations of buildings in swampy sites…remains undecayed for eternity, bearing immense loads of masonry and preserving them flawless.” 

In summer, after the Seine’s flow had been diverted from the worksites by cofferdams, long piles were driven into the riverbed to about two thirds of their length. The tops of the piles, projecting up to the usual river level, were encased and sealed in caissons of wooden planks. Then, concrete was poured into this formwork, locking the groups of piles in place. The bridge of stone piers and arches was constructed on these foundations, and along each side of the bridge were shops and houses.

The concrete included lime and siliceous sandstone, in effect similar to Roman pozzolanic concrete. This was the first recorded use of hydraulic concrete since the Roman Empire.

Fra Giocondo had proved that making pozzolanic concrete doesn’t need a volcano. He went on to publish the first illustrated version of Vitruvius’ De Architectura, and it was widely printed in contemporary European languages. Both author and publisher, and Pont Notre-Dame too, became an inspiration for experiments and trials in new mixes of concrete during the Industrial Revolution.   

The foundations of Pont Notre-Dame never failed. In 1853, the stone arches were demolished and replaced by new ones, but they rested on the original foundations. Then, in 1914, this new bridge was itself replaced by the existing iron and steel one, without piers. The old foundations went quietly into early retirement after four hundred years.      

Afterword

Dear reader, I was about to send this piece off to TFE when I overheard four gentlemen chatting over a glass of vinum…. The Elder and Younger Plinys, Vitruvius and Fra Giocondo apparently. They sounded happy to have their books remembered, but they wanted to make a point. Yes, they said, “cement and concrete can be astonishing and magnificent – just look at the Sydney Opera House – but Houston, we have a problem. The Fall of Rome was nothing compared to what climate change may do…. We are turning nature against ourselves. And with ordinary cement emitting its own weight in CO2, they said, plus the increasing use of concrete, everyone in the business had better keep innovating. And let’s hope we don’t have another Dark Ages”. I said I’d pass that on.  

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Oliver was a film director and writer at Film Australia, for the Papua New Guinea government, and as an independent producer. He has worked in Japan and in Pacific Island states, and with Aboriginal Communities in Western Australia, the Northern Territory and in Sydney. He has been an aid volunteer in Timor-Leste and in Sydney and has written for newspapers and websites.