After the Romans conquered Britain in AD 43, they brought with them technologies and laws that led to centuries of economic growth once thought to be limited to modern industrial societies, according to an analysis of thousands of archaeological finds from the period.

“In about 350 years, about two and a half years [fold] “Improved productivity per person.” Rob Weisman At Cambridge University.

Wiseman says the ancient world long believed that economic growth depended on increases in population and resources — for example, increasing food production required more land and more agricultural workers — a type of growth known as extensive growth.

In contrast, economic growth today is driven primarily by increases in productivity, or intensive growth: for example, mechanization and improved plant and animal breeding enable us to produce more food from the same amount of land with fewer workers.

Several recent studies have challenged the idea that rapid growth only occurred after the Industrial Revolution began, which led Wiseman and his colleagues to look at growth in Roman Britain from 43 to 400 AD.

Wiseman says the team’s research was made possible by British laws that require archaeological investigations when sites are developed. “As a result, tens of thousands of archaeological excavations have been carried out in this country, and the data is available to the public.”

By looking at how the number of buildings changed over time, the researchers were able to get a sense of how the population of Roman Britain grew — and there’s a strong relationship between the number of buildings and population size, Wiseman says.

To get a sense of economic growth, the team looked at three metrics: First, the size of buildings rather than the number of buildings: As people get wealthier, they build bigger homes, Wiseman said.

Another measure is the number of lost coins found at the excavation site: “That fell through the floorboards, that got lost in the bathroom, that sort of thing,” he says.

The idea is that the more coins there are in circulation, the more likely they are to be lost. The team didn’t count hidden hoards of coins because they reflect instability, not growth.

The third criterion is the ratio of cruder pottery, such as cooking and storing pots, to more ornate pottery, such as decorative plates. Economic growth requires people to interact more and socialize more, which means “showing off” when guests are present, Wiseman says.

Based on these indicators, the team found that economic growth exceeded what would be expected from population growth alone. They estimate that per capita growth was about 0.5% between 150 and 250 AD, slowing to about 0.3% between 250 and 400 AD.

“What we’ve been able to show is that there was indeed rapid growth after the Romans arrived,” Wiseman says. The rate of growth, rather than the type of growth, is likely what distinguishes the modern world from the ancient world, he says.

Researchers believe this growth was driven by factors such as roads and ports built by the Romans, laws they introduced that made trade safer, and technology such as more advanced flour mills and animal breeds suited to farming.

The period of rapid growth between AD 150 and 250 could have been the result of Britain catching up with the rest of the Roman world, Wiseman says: “It went from being a small, poorly-connected tribal society to a global economy.”

What’s not clear is whether this economic growth made people happier or healthier. “The fact that productivity rose doesn’t mean that invaded, colonized Britons were better off under the Roman Empire,” Wiseman says. “That’s an open question.”

To investigate this, researchers now plan to examine human remains to determine things like how long people lived.

“I believe they are right, and there was certainly intensive growth in Roman Britain.” Alain Bresson At the University of Chicago, Illinois.

“Many archaeologists have noted the compelling evidence of economic growth in Roman Britain, but this paper adds a welcome formal theoretical dimension to the debate.” Ian Morris At Stanford University, California.

But Morris suspects that the lower average growth rate from A.D. 250 to 400 actually reflected a period of higher growth that declined sharply as the Roman Empire began to collapse. Further research could help find the answer, he says.