How Societies Lose Innovations

The Pantheon in Rome was completed in 126 CE, under the rule of Hadrian, as a Roman temple. The structure is an architectural marvel. It is the world’s largest unreinforced concrete dome, and for 1300 years was the world’s largest dome.

The Pantheon was built with bricks and concrete. The Romans used concrete everywhere to build magnificent structures that were a testament to their grand ambitions and vision, and architectural ingenuity.

Roman concrete is widely known to be of extreme durability — such that many structures the Romans built are still standing today, 2,000 years later — when even modern concrete structures may only last years or decades.

Yet following the fall of the Roman Empire in 476 CE, use of innovative Roman concrete almost entirely disappeared from the world.

How is it that innovations can be lost in society, and what lessons can be gleaned?

Roman Concrete is Unique, Even Today

The Romans did not invent concrete, but they were the first to use it on mass scale. Its three primary ingredients were lime, volcanic ash, and water. When mixed with rubble it could be used to create walls.

Part of the strength of Roman concrete was due to luck. The volcanic ash from Pozzuoli, on the Bay of Naples, was considered a key ingredient and was shipped across the Roman Empire for use in construction.

It was also due to Roman technique. In 2023, a team of researchers from MIT and Harvard discovered that Romans used lime in a more reactive form called quicklime. When integrated with water it would leave lumps. These lumps powered the concrete’s strength. When the concrete would crack, rainwater would gather in the crack and dissolve the lumps, which would the recrystallize and restore the concrete.

Romans also figured out that adding seawater strengthened the concrete even more; scientists recently learned this was due to the seawater dissolving the volcanic ash, allowing new binding materials to grow. This knowledge led to the building of the world’s largest artificial harbor at Caesarea.

With their ultra durable concrete, Romans were able to build magnificent structures: temples, public baths, aqueducts, and bridges. The Colosseum, built on marshland, would have been impossible to construct without concrete.

Loss of Innovation

As the Roman Empire declined, so did the use of Roman concrete to build grand structures. The last spectacular concrete building of this monumental era was the Basilica of Maxentius, finished in 313.

Sometimes innovations wane because something better is invented to replace it, or because society’s interest veers in a new direction. That happened here, too.

The largest benefactor to replace the Roman Empire was the Church, but the architectural design of large churches was different and had little use for concrete. The Hagia Sophia of Istanbul, built in 360, was initially a domed church but was made of brick, adhering to preferred local customs.

But the decline of Roman concrete was also symptomatic of something broader.

Whether it is building the Pantheon, landing a man on the moon, or colonizing Mars, achieving great feats in a society requires bold ambition, political and economic means, and national purpose.

The decline of the Roman Empire coincided with political and economic collapse that included the emptying of cities and return to simpler, agrarian lifestyles. Among the local tribes there was simply interest, vision, or means to build grandly.

With the collapse of trade in the Western Roman Empire there was neither need nor ambition to build new harbors. Society turned inward.

The Eastern (Byzantine) Empire soon followed. Justinian used concrete to build a new harbor in Constantinople in the 6th century, but subsequent political turmoil ended large construction projects there for the next 200 years.

Knowledge for how to create Roman concrete persisted through historians and authors such as Pliny the Elder, Vitruvius, and Isidor of Seville, but this was mostly left to collect dust as an historical record, not as practical knowledge to spurn new construction.

The persistence of great societies is not inevitable, they must be continually renewed and restored. The story of Roman concrete is a small example of what is lost when they end.

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