Ancient melons in East Asia likely arrived from South Asia,

 Melons produce many seeds, making the melon shape a traditional symbol of fertility and prosperity in Chinese culture. But the historical debate about how melons made their way to modern tables is as long and twisted as the vines they grow on.

A new study published in Proceedings of the National Academy of Sciences reveals newly discovered aspects of melons’ ancient history. Based on an analysis of the ancient DNA of seeds from a Song imperial dynasty archaeological site in southeastern China (circa 960-1279), scientists at Washington University in St. Louis have determined those ancient melons in East Asia likely arrived from South Asia, rather than being developed from wild Chinese plants, and that they lacked the sweetness of modern dessert melons.

These melons’ flesh color likely resonated with Song dynasty aesthetic sensibilities, as seen in jade-green celadon ceramics that were locally crafted in melon-shaped forms.

Taken together, the study offers a rare and compelling example of how cultural tastes and crop traits may have influenced each other, the researchers said. The study is also an example of how scientists can use ancient DNA to answer historical questions beyond what macro-botanical evidence or artifacts alone can reveal.

Biologist Susanne Renner, in WashU Arts & Sciences and co-author of the new PNAS study, has studied melons for more than 25 years. “At that time, it was assumed that because the genus Cucumis, to which melons belong, has numerous wild African species, that melons originated in Africa,” she said. 

But Renner was never convinced. In 2010, she published a study based on some 100 Cucumis samples from Africa, Australia and Asia that showed that melon has numerous previously overlooked species-level relatives in Australia and around the Indian Ocean. “Based on biogeographic analysis, we inferred that melons most likely originated in Asia, not Africa,” Renner said. It is now clear that melon domestication has occurred independently once in Northeast Africa and twice in India, but archaeobotanical evidence points to a possible additional domestication event in southeastern China.

Renner worked with colleagues in Germany and the United Kingdom on the analysis that the melons came from South Asia, rather than locally domesticated despite older archaeological evidence in the region, warranting further investigation. There are two paths they might have taken, the researchers said: a northern “Silk Road” along the foothills of the Inner Asian Mountains and the northern margin of the Tibetan Plateau, or a southern “Tea Horse Road” along the southern slopes of the Himalayas and through the valleys of southwest China. 

“Both corridors are historically plausible, as demonstrated by the movement of other food resources,” Liu said. “Current archaeological evidence points more strongly to a southern route. The earliest melon remains in China have been recovered from Han and pre-Han royal tombs in southern China, predating comparable finds from northern ‘Silk Road’ sites by approximately 800 to 1,000 years. We therefore consider a southern route connecting southern China with Southeast and South Asia to be a candidate for the early introduction of melon into China.”

Their genomic analysis also revealed other intriguing facts about the kinds of melons grown in China in the 10th to 13th centuries. 

“The color-related traits are particularly interesting. They suggest that these ancient melons likely had light-green flesh and yellow peel,” Liu said. “Melons with these characteristics are often consumed as vegetables, as mildly sweet fruit, or for their seeds, rather than as high-sugar dessert melons. In the lower Yangtze region today, culinary traditions of consuming melon as pickles or vegetables still persist.”

Liu and Renner said that even today, there are only a handful of crops for which ancient DNA has been obtained and placed in context with the evolution of specific traits. These include the economically important crops of barley, certain types of wheat, cotton, maize and beans. “The difficulty lies in the generally very few substitutions that can be attributed to selection on specific traits,” Renner said. 

The melon’s flesh color itself may have held cultural and symbolic significance during the Song Dynasty, Liu said. 

“The light-green color resonates with the fine-toned color of Chinese jade and with the glazes of celadon porcelain, both highly valued in East Asian aesthetic traditions,” he said. “During the Song dynasty, green celadon ceramics produced in the lower Yangtze region and beyond were frequently fashioned in melon-shaped forms, with glazes echoing the jade-green tones of melon flesh.” 

Such greenware ceramics was popular across East Asia, including China, Korea and Japan, and many examples were recovered from Gugang, Liu said. It might have been popular across the region due to the melon’s symbolic value of fertility and abundance.

“Taken together, this represents a rare and compelling case of cultural-genetic symbiosis, reflected in the parallel historical selection of melon traits and celadon aesthetics,” Liu said.

Which is why Renner was intrigued when she sat down next to WashU colleague Xinyi Liu, a professor of archaeology in Arts & Sciences, at a WashU Living Earth Collaborative event. Liu told her about many archaeological seeds, including those that were recently uncovered in an excavation of a medieval port in southeastern China.

Located in present-day Wenzhou, the Gugang port (Shuomen Gugang) helped connect continental East Asia with the Pacific and Indian Ocean worlds during the Song dynasty. An archaeological excavation of the port in 2024 uncovered sunken shipwrecks with large quantities of porcelain and imported fruits such as grape, olive, lychee, kiwifruit — and melons.

Amid this submerged world, Liu saw opportunity. Ancient genetic research relies on exceptionally favorable preservation conditions, where plant DNA are likely to survive. The waterlogged deposits at Gugang represented one such location.

 

Preehistoric builders hauled 25-ton stones 18km to build Britain’s tallest stone row

 

Peer-Reviewed Publication

Curtin University

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Devil's Arrows, Yorkshire. Credit - Dr Jim Leary

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Credit: Dr Jim Leary

New research has revealed ancient builders deliberately transported enormous 25-tonne stones across at least 18 kilometres (11 miles) to build Britain’s tallest surviving prehistoric stone row - the iconic Devil’s Arrows.

The Curtin University-led study, in collaboration with the University of York, UK, is the first to identify the geological source of the towering stones, tracing them to the rugged terrain of Brimham Rocks in North Yorkshire.

The Devil’s Arrows, located near Boroughbridge in northern England, stand up to seven metres tall and form a rare stone alignment in a lowland setting. Despite their scale and prominence, their origins have remained a mystery until now.

The stones are believed to have been transported and erected during the Late Neolithic or Early Bronze Age, possibly around 2000 BC.

Lead author Dr Anthony Clarke, from the Timescales of Mineral Systems Group within Curtin’s School of Earth and Planetary Sciences, said the findings challenged long-held assumptions about how and why ancient monuments were built.

“Our research shows these stones weren’t simply taken from the nearest available source - they were deliberately chosen from a challenging landscape 18 kilometres away,” Dr Clarke said.

“Plumpton Rocks, which is closer to the Devil’s Arrows, had previously been identified as the probable source of the stones. Our findings instead point to Brimham Rocks, showing that prehistoric builders transported these enormous stones significantly further than thought.

“Each stone weighs more than 25 tonnes, so moving them would have required incredible planning, coordination and engineering skill.

“This tells us prehistoric people placed real importance on the landscape itself. It wasn’t just about convenience - the location the stones came from likely held meaning for them.”

Co-author Dr Jim Leary from the University of York said the findings reshaped how researchers understood prehistoric monument-building.

“These results show that ancient communities were making deliberate and meaningful choices about where their stones came from,” Dr Leary said.

“It highlights the importance of landscape and shared belief systems, as well as the remarkable effort involved in transporting and raising stones of this size.”

The team used a new low-impact sampling method involving adhesive tape to collect tiny mineral grains from the stones without causing damage. By analysing the age “fingerprints” of these grains, researchers were able to match the stones to their source at Brimham Rocks.

The results also rule out natural processes such as glacial movement, demonstrating that the stones were intentionally transported by people.

Dr Clarke said the research team planned to apply their non-invasive method to other standing stones with unknown origins and conduct targeted excavations at both the monument and its newly identified source site.

“These next steps could help us better understand when the stones were moved and how these extraordinary monuments were constructed,” Dr Clarke said.

Justin Scully, National Trust General Manager for Fountains Abbey & Studley Royal and Brimham Rocks, said the research reveals a direct link between Brimham Rocks and the Devil’s Arrows, connecting two remarkable Yorkshire landscapes.

“We’re incredibly grateful to the researchers for helping us uncover this new chapter in the stones’ story and deepen our understanding of the people who shaped this landscape thousands of years ago,” Mr Scully said.

“The Devil’s Arrows are deeply cherished by local communities, and we’re delighted that this discovery adds a new chapter to their story.”

The study, ‘Deliberate Prehistoric Sourcing of the Devil's Arrows, Britain's Tallest Stone Row’, was published in the Proceedings of the Royal Society A (https://doi.org/10.1098/rspa.2026.0504).

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Did wildfires help spark the invention of pottery?

 

Peer-Reviewed Publication

The Hebrew University of Jerusalem

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Tens of meters in thickness at Nahal Arava, in the center of the southern Dead Sea basin )31.263003N, 35.395929E(, it comprises mainly lacustrine clastics reaching. The white aprons are redeposited salt minerals leached from Dead Sea salt layers. Note persons on top, for scale. The Ze'elim Formation represents the thick deposits at base level sediment traps.

 

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Credit: Credit: Amos Frumkin

A new study suggests that a period of intense fires and landscape upheaval in the ancient southern Levant may have helped create the conditions that led Neolithic communities to discover how fire could transform clay.

Thousands of years before pottery became an everyday part of human life, communities in the southern Levant were living through a period of dramatic environmental change. Hillsides burned, vegetation disappeared, soils were stripped away, and enormous quantities of clay-rich sediment washed down into valleys.

According to a new study by Prof. Amos Frumkin of the Institute of Earth Sciences at the Hebrew University of Jerusalem, those destructive events may also have helped inspire one of humanity's most important technological innovations: pottery.

Published in Geomorphology, the study brings together evidence from ancient sediments, caves, charcoal deposits and archaeological sites to reconstruct how wildfires and erosion reshaped the southern Levant during two periods of major environmental instability. Prof. Frumkin proposes what he calls the "natural kiln hypothesis": Neolithic communities may have learned that clay could be permanently hardened by fire after witnessing naturally baked clay produced during intense fires.

When the Landscape Burned

The study compared two periods separated by more than 100,000 years.

The first was the last interglacial period, known as MIS 5e, roughly 129,000 to 116,000 years ago. The second was the early Holocene, between approximately 11,000 and 7,000 years ago, when farming communities were becoming increasingly established across the region.

Evidence from both periods points to episodes of extensive wildfire followed by severe erosion. Tiny charcoal particles preserved in ancient lake sediments record peaks in burning, while chemical signatures preserved in cave formations indicate substantial losses of vegetation and soil. During the early Holocene, the most intense episode appears to have occurred around 9,500-8200 years ago.

Although Neolithic and earlier people have deliberately used fire on a limited scale, Prof. Frumkin argues that the geographical extent and timing of the fires point to climatic causes for increasing use of fire.

Once vegetation disappeared, exposed soils were vulnerable to rain and runoff. Clay-rich terra rossa soil was swept from the hills and deposited in enormous quantities in depressions, such as the Jordan and Dead Sea valleys. Instead of simply destroying habitable land, however, this process created new environments where farming communities could flourish. Large Neolithic settlements increasingly clustered on these fertile redeposited soils.

Could Nature Have Demonstrated How to Make Pottery?

The study offers a new explanation for the emergence of ceramics.

Pottery appeared in the region during roughly the same broad period in which fires, erosion and clay deposition reached their peak. Prof. Frumkin proposes that people living in the valleys may have encountered patches of clay that had been exposed to intense natural fires and noticed that heat had transformed the soft material into something hard and durable.

That observation could have provided the basic idea behind intentionally firing clay.

The hypothesis is supported by earlier petrographic research showing that Yarmukian pottery from the Jordan Valley was manufactured from local redeposited terra rossa clay, the same material that would have accumulated around settlements following the erosion of nearby hills.

“A wildfire is normally seen only as a catastrophe, but environmental disruption can also expose people to new materials and new possibilities,” said Prof. Frumkin. “Neolithic communities in the Jordan Valley may have watched fire transform the clay beneath and around their settlements and realized that this process could be reproduced deliberately. If so, one of humanity’s most important technologies may have emerged partly from people learning to imitate what they had already seen nature do.”

Pottery would eventually transform daily life, making it easier to cook, store food and liquids, ferment products and support larger settled communities. Decorated vessels and figurines also became important cultural objects, suggesting that ceramics quickly acquired significance beyond their purely practical uses.

A 120,000-Year-Old Natural Experiment

One of the most intriguing pieces of the argument comes from a much earlier period.

During the last interglacial, which predated the last glacial period, the southern Levant experienced an even more extreme combination of fires, vegetation loss, erosion and clay deposition. Yet pottery did not appear.

Prof. Frumkin describes this earlier period as something of a natural control experiment. The environment produced many of the same ingredients, but the people living in the region did not have the cognitive abilities, sedentary agricultural society, technological knowledge and social conditions that later Neolithic communities possessed.

The comparison suggests that nature alone did not invent pottery. Instead, technological innovation may have emerged when environmental opportunity met a society capable of recognizing and exploiting it.

A Hypothesis Still Waiting to Be Tested

Prof. Frumkin stresses that the natural kiln hypothesis remains speculative and testable, rather than a proven account of pottery's invention. The available evidence establishes that major fires, clay deposition and the emergence of pottery occurred within the same broad period, but current dating cannot yet demonstrate the exact sequence of events.

Future archaeological excavations could search beneath the earliest pottery-bearing layers for naturally fire-baked clay. Experimental research could also test whether wildfires in the Jordan Valley could have heated clay to the roughly 500 to 700 degrees Celsius needed to begin permanently transforming it into ceramic material. Finding pottery that clearly predates the major fire episode would, Prof. Frumkin notes, challenge the hypothesis.

Rather than replacing existing theories that pottery developed through gradual experimentation, social needs or contact between communities, the study proposes another possible piece of the puzzle: environmental catastrophe itself may sometimes create opportunities for innovation.

In conclusion, the fires that stripped ancient hillsides of their soils may also have reshaped where people lived, how they farmed and, potentially, how they learned to turn earth into pottery.

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DOI

10.1016/j.geomorph.2026.110514 

Consistent heel-to-toe steps set early humans apart from other great apes

 and helped enable efficient foraging strategies like hunting and gathering, according to new research

 The average person takes thousands of steps each day, instinctively walking heel-to-toe. Although they hardly register them, those consistent heel-first strides are more unique to humans than previously thought and allowed early hominins to walk farther more efficiently, but at the cost of higher impact forces on bones and joints, according to a new study led by a researcher at Penn State.

The team said the findings, published today (Sept. 8) in the Proceedings of the National Academy of Sciences, shed light on an evolutionary adaptation that made early human walking more efficient, ultimately helping our ancestors to adopt hunting and gathering practices and spread across the world.

Previous research relying on descriptive data has suggested that humans share the heel-first, or heel-strike, walking style with other great apes like the closely related chimpanzee. The authors of the new study used high-speed, high-resolution video equipment and a flat runway lined with metal plates that measure impact forces to examine how chimpanzees and humans walk.

They found that chimpanzees vary their walking style, landing on the side or ball of their foot a majority of the time and landing heel-first less often when walking on two legs compared to moving on all fours. Humans, on the other hand, always land with a heel-strike. The researchers found that this walking style saves modern humans an estimated 26% to 41% of the metabolic energy it would take to walk on the ball of the foot but results in higher impact forces, which required bigger, stronger bones and joints — later adaptations that would allow early humans to cover more ground in a safe, consistent way.

“When people think about what makes human walking unique, they talk about upright walking — our backs are straight and our legs are extended,” said study author Nicholas Holowka, assistant professor of anthropology and co-hire with the Huck Institute of Life Sciences at Penn State. “What we’re saying in this article is that landing on our heel is a unique aspect of human walking that’s maybe been underappreciated. This study presents the best measurable comparison of humans to our closest living relatives, chimpanzees, which shows that what we’re doing when we land is distinctive in key ways.”

The earliest human ancestors likely walked the way chimpanzees do — with less consistent, more variable landings, sometimes on the balls of their feet or flat-footed, other times on their heels, said Holowka. He described the walking style as less efficient than that of modern humans and explained that it probably confined how far they could travel. The heel strike, he continued, is much more efficient, allowing humans to roll from the back of the foot to the front for a smooth ride. But it comes with the tradeoff of higher impact forces, that cause more rapid loading on the leg. 

“Imagine you are trying to sneak across a creaky wooden floor,” said study co-author Nathan Thompson, an associate professor at New York Institute of Technology, College of Osteopathic Medicine. “You tend to walk on the balls of your feet, because this reduces the rate of loading on the floor and creates less creaking. It’s a softer way to walk.” 

These more impactful forces could have potentially been damaging to the body and ultimately required later adaptations to allow early humans to walk in a safe, consistent way, according to the researchers.

“It seems like humans needed to evolve anatomical adaptations — thicker heel bones and bigger knee and ankle joints — to cope with these high forces,” Holowka said. “We think that the heel-strike played a role in enabling key human behaviors, such as using hunting and gathering strategies that require people to walk really long distances every day to get food, but for a big payoff in food resources.”

The researchers used high-speed, high-resolution cameras and an approximately 36-foot-long walkway lined with metal force plates at Stony Brook University to examine how three male chimpanzees walked on all fours and on two legs. They augmented their data collection by analyzing walking data from three more chimpanzees collected by another research team in a separate study and reviewed additional data from two other studies from a combined 15 chimpanzees.

The team also recruited 12 human participants for similar laboratory experiments at the University at Buffalo. Nine participants wore reflective markers and walked barefoot on an approximately 25-foot-long runway lined with force plates and high-speed, high-resolution cameras. These participants walked the runway multiple times, using their natural gait as well as an altered gait that mimicked the way the chimpanzees preferred to walk, landing on the ball of the foot just behind the little toe before bringing down the heel. The researchers referred to the latter style as midfoot-strikes. The human participants also walked on a treadmill while wearing a portable respirometry system that measured oxygen consumption and carbon dioxide production. They used these measurements to calculate how much energy the participants expended using the different walking styles.

The researchers found that the chimpanzees varied their walking style, using a mix of heel-strikes and midfoot-strikes. However, they used fewer heel-strikes when walking on two legs than when walking on all fours. 

“It seems that when walking on two legs, chimpanzees prefer the ‘softer’ way to land on their feet,” Thompson said. 

All normal gait human steps, however, were heel-strikes, with the angle of foot contact relative to the ground very consistent within and between individuals. Chimpanzees, on the other hand, used 2.4 to 8.6 times greater ranges of foot-strike angles than the human participants, the researchers reported.

The team also found that the heel-strike generated much higher impact forces than midfoot-strikes in both chimpanzees and humans. In chimpanzees walking on two legs, the rate of impact force loading ranged up to 138% higher for heel-strikes than midfoot-strikes. In humans, these forces ranged up to 162% higher than midfoot-strikes. However, walking heel-first saved the human participants an estimated 26% to 41% in expended metabolic energy compared to midfoot-strikes. 

“We humans have evolved to use this high-impact walking style in a way that is safe and natural for us,” Holowka said. “The novel environments that we currently live in with their hard, paved surfaces might upset the evolutionary balance in some ways. It’s something that we’d be interested in looking at in future research. Still, walking a lot is a very healthy exercise and, although high impact, our bodies evolved to cope with it, so we shouldn’t avoid it.”

Penn State doctoral students Zacchariah Apolito and Kevin Palmisano contributed to this work. Other study co-authors include Matthew O’Neill, Midwestern University; Vincent Bhandal, Otto Lam and Brigitte Demes, Renaissance School of Medicine at Stony Brook University; Caleb Massimi, Icahn School of Medicine at Mount Sinai, New York; and Steven Worthington, Harvard University.

The research was funded by the U.S. National Science Foundation under grant BCS-0935321, the Leakey Foundation and the Wenner-Gren Foundation. This content is the responsibility of the authors and does not necessarily reflect the views of the funders. 

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2533918123 

Agricultural diffusion, population movement, and funeral practices in ancient Gansu

 

A multidisciplinary study has answered key questions about how agricultural practices diffused into ancient Gansu from Eurasia, as well as described population movements and funeral practices in the Gansu region thousands of years ago.

Gansu, now a province in northwestern China, has long been a key crossroads for transcontinental exchanges of domesticated crops and livestock. Yet it has not been clear whether such exchanges were driven by human migration—a process known as demic diffusion—or by the introduction of crops and livestock to existing populations—a process known as cultural diffusion.

Now, researchers using genomic data from 149 ancient human individuals in Gansu, have shown that the introduction of western-derived agriculture amid waves of trans-Eurasian exchange was not accompanied by direct demic diffusion.

The study, which was published in Cell on September 3, was conducted by a research team led by Professor FU Qiaomei from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences (CAS), working in collaboration with multiple institutions.

The genomic data used in the study date to around 4,700–3,000 years ago—a critical period when cereals and livestock first domesticated in western Eurasia were being introduced to the region.

According to the researchers, the results did not detect any traces of genetic influence from western Eurasia or Central Asia among the ancient individuals, despite the adoption of western-derived crops or livestock at nine of the 11 Gansu sites.

Instead, the dominant genetic ancestries detected in Gansu were linked to populations that once inhabited the Yellow River basin, the southeastern Mongolian Plateau, and the Tibetan Plateau. A few genetic outliers also pointed to interactions between Gansu and regions both nearby and farther north, including the cis-Baikal area.

These results suggest that the introduction of western-derived domesticates did not involve a direct large-scale western population influx—unlike patterns of agricultural expansion found in Europe and Central Asia. Possible explanations for this phenomenon chiefly include cultural diffusion through the Inner Asian Mountain Corridor, or transmission via exchange networks or intermediary populations across the Mongolian Steppe.

Unveiling Social Practices in Ancient East Asia

In addition to the genetic focus, the study also included information on Late Neolithic and Bronze Age social and burial practices, based on investigation of the large cemetery at Mogou (3,600–3,200 years before the present)—one of the largest excavated cemeteries in China.

The researchers noted that genetic similarities among the Gansu sites revealed a broad correlation—though not a strict alignment—between genetic ancestry and archaeologically defined cultural groups.

Through kinship and identity-by-descent (IBD) analyses, most Mogou individuals were found to form a broadly linked network based on biological relatedness that persisted through the transition from the Qijia to the Siwa archaeological cultures, pointing to a continuous and connected society.

The researchers also found evidence of endogamy at Mogou, as two individuals showed signs of parental consanguineous mating, while runs of homozygosity segments hinted that Mogou may also have practiced some level of exogamy, finding some mates from outside communities. Furthermore, female and male individuals at Mogou did not exhibit significant differences in relatedness, suggesting that the Mogou community did not strictly maintain either patrilocal or matrilocal residence patterns.

By integrating burial practices and genetic patterns, the results showed that genetic outliers—individuals who were not close biological relatives of core community members—were more likely to be buried in settings archaeologically interpreted as lower-status. As for biological sex, while males were predominantly buried with food production tools and females with spinning wheels, no significant differences were found in other burial practices analyzed, such as burial location or the number of funerary objects.

Surprisingly, no strong correlation emerged between genetic relatedness and burial distance among the sampled burials in the cemetery. Within tombs containing multiple burials, no first- or second-degree relatives were found buried together, and some co-buried individuals may have had mixed social status or have been interred at different times.

These results imply that burial customs at Mogou were not strictly centered on biological relatedness, and that other interpersonal relationships, along with the repeated use of tombs over different time periods, likely also played a role in determining who shared a tomb.

According to the researchers, this multidisciplinary study provides important insights into population movements amid waves of trans-Eurasian exchange—demonstrating that the introduction of western-derived agriculture was not accompanied by direct demic diffusion—while also shedding light on the extensive kinship networks and complex burial customs of the local community at Mogou.

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Journal

Cell

DOI

10.1016/j.cell.2026.07.050 

Article Title

Traces of nearly four million coins reveal how Rome achieved economic integration

 

For centuries, the study of ancient history relied primarily on interpreting classical texts and examining inscriptions and archaeological remains at their sites of origin or in museums. In recent years, however, a little-known transformation has profoundly changed this landscape. The digitization of extensive archaeological collections, coupled with the development of quantitative methods that can integrate millions of scattered records, is ushering in a new era of historical research. Like other scientific disciplines that have benefited from processing colossal amounts of information, archaeology and history have entered the era of data science.

Two researchers from the Regional and Urban Economics Lab at the University of São Paulo (NEREUS-USP) in Brazil have just presented an example of this approach. Using techniques from regional economics, spatial analysis, geographic information systems, and large international archaeological databases, they reconstructed the monetary circulation of the Roman Republic, focusing on the period from 155 BCE to 2 CE, based on the remains of approximately four million coins found in excavations conducted over two centuries. Their study shows that the consolidation of Roman rule depended less on military conquest and more on the economic integration of the territories they conquered.

The research was conducted by Eduardo Amaral Haddad, a professor at the School of Economics, Business, and Accounting (FEA-USP), and Inácio Fernandes Araújo, currently a professor at the Luiz de Queiroz College of Agriculture (ESALQ-USP). The two authors published an article in the journal Humanities and Social Sciences Communications, which is part of the Nature group.

The research seeks to understand how coins reflect the functioning of a growing economy, going beyond simply tracking their movement. “Each coin preserved by archaeology provides three key pieces of information: where it was minted, when it was produced, and where it was found some 2,000 years later. Taken in isolation, that information reveals little. However, when millions of records are analyzed together, they can reveal the paths taken by money, the intensity of economic exchanges, the integration between different regions, and even the institutional evolution of one of the largest economies of antiquity,” says Haddad.

The research was supported by FAPESP through two projects (14/25030-2 and 19/00057-9).

A study that began as a hobby

The project originated in 2014 when Haddad, already a professor at FEA-USP, took a sabbatical at Princeton University in the United States. Although he was conducting research in economics, he began attending a weekly seminar organized by the Department of Classical Studies out of personal interest.

“At one of those meetings, I attended a presentation of a study that used shipwreck remains and pottery shards to reconstruct trade networks in the ancient Mediterranean. That idea stuck with me. Shortly thereafter, while exploring the university library, I found a catalog of Roman coins that contained the information I needed: the date of minting, the location where each coin was produced, and the site where it was found during archaeological excavations. I photocopied the catalog, thinking it would be possible to analyze those networks using tools from regional and urban economics,” he recalls.

That initial interest eventually turned into a long-term project. To deepen his knowledge of the classical world, Haddad enrolled in a distance-learning graduate program on the ancient Mediterranean offered by the University of Leicester in the United Kingdom. One of the papers he wrote during the program became the basis for a published article.

Computational archaeology

For a long time, information on Roman coins was scattered among museums, libraries, private collections, and researchers’ archives. This fragmentation hindered attempts to reconstruct large-scale circulation patterns. However, the situation began to change when institutions such as the American Numismatic Society started coordinating international projects to digitize and standardize these collections. These projects established common protocols for recording archaeological information. Today, large public databases bring together millions of records from excavations conducted in different countries.

“The main source for our study was Coin Hoards of the Roman Republic Online [CHRR], a database dedicated to coin hoards from the Roman Republic. The study also drew on various digital archaeology platforms. Among them was ORBIS, developed by Stanford University [United States], which simulates travel along the network of roads, rivers, and sea routes of the Roman world and estimates the time and cost of journeys between hundreds of locations. The study also included the Pleiades gazetteer and the Roman Road Network databases, which provided georeferenced information on cities, roads, and ports in the ancient Mediterranean,” Haddad explains.

These databases were integrated into a single spatial analysis system. After a careful curation process, the researchers began working with a set of approximately four million coins organized into 24,646 hoards corresponding to 5,167 pairs of minting and discovery sites. Rather than analyzing the coins individually, the researchers chose to use these archaeological records, thereby reducing distortions caused by differences in their preservation, loss, or reuse over the centuries.

However, the goal went far beyond simply creating maps. “We needed to consider that circulation from the perspective of human interaction in space according to an economic logic,” Haddad explains. It was at that moment that his expertise in regional economics found an unexpected application. The same mathematical tools developed to study contemporary flows of people, goods, and income were used to investigate monetary movements that occurred more than 2,000 years ago. Instead of analyzing modern cities, the focus shifted to the Roman Mediterranean. Instead of tracking contemporary supply chains, the researchers sought to reconstruct the economic networks that sustained Rome’s expansion during the last two centuries of the Republic.

Follow the money

The Roman Republic is conventionally dated from 509 BCE to 27 CE, when Octavian Augustus established the Principate. The last two centuries of the Republic therefore correspond to the period between 200 and 27 CE, which encompasses the consolidation of Roman hegemony following the Second Punic War (218–201 CE), the conquest of the Hellenistic Mediterranean, and the expansion into Hispania, Gaul, the Balkans, and the East. This period also includes the civil wars that led to the end of the Republic.

The researchers’ first question was simple yet decisive: Was the spatial distribution of the coins random, or did it follow a pattern? To answer this question, the team employed spatial analysis techniques widely used in regional economics and economic geography. The tests showed that the findings were far from random. On the contrary, the coins formed statistically significant clusters concentrated along the main trade routes of the Roman world.

Once this initial result was identified, an even more ambitious question arose: Would it be possible to reconstruct the paths taken by the money? “After verifying a correlation between the location and concentration of the coins, we began to cross-reference that information with Roman roads. And we found something very interesting: a clear spread of coins originating from Rome,” says Haddad.

The maps produced by the study show that monetary circulation closely followed the infrastructure built by the Roman Republic. Roads, ports, and major urban centers were not just thoroughfares; they were the channels through which the economic relations that sustained territorial expansion spread.

However, tracing the path of the coins was only the first step. The next question was why some regions had intense monetary circulation while others remained relatively peripheral.

“Answering that question required more than maps. It was necessary to reconstruct – albeit approximately – the functioning of the Roman economy itself. To do so, we organized information from historical and archaeological literature into a model inspired by so-called social accounting matrices, a tool used to analyze contemporary economies. The model describes the relationships among the main economic actors of the time: the government, households, landowners, merchants, slaves, and the army. It seeks to represent the flows of goods and payments that linked those institutions. It also distinguishes between different types of production and consumption, ranging from food and raw materials to manufactured goods and luxury items, the trade in which could extend over much greater distances,” Haddad reports.

Another aspect incorporated into the model was the gradual monetization of the Roman economy. During part of the Republic, many transactions continued to be conducted in kind. Over time, however, payments related to supplying the army, maintaining slaves, and various public activities progressively began to be made in coin. This transformation left its mark on the archaeological collections themselves. Based on this economic model, coin hoards found in excavations ceased to be mere collections of ancient coins. Instead, they are treated as material evidence of the economic relationships that structured the Roman Republic.

First the army, then the economy

At this point, one of the most interesting conclusions of the study emerged. A widely held interpretation attributes the Roman army the predominant role in disseminating currency throughout the conquered territories. This assertion seems intuitive. As the legions advanced, they brought with them soldiers who received wages and suppliers who traded goods, generating intense monetary circulation. However, the results only partially confirm this hypothesis.

According to Haddad, military structures played a decisive role in the initial phase of expansion. However, their influence waned as the new territories were permanently incorporated into the Roman world. “What we realized was that military expansion introduced monetary circulation, but it only became established once those territories were effectively integrated, creating economic, religious, administrative, and civic structures capable of generating a permanent demand for currency,” he points out. In other words, the army served as a catalyst for opening up these regions. It was the economy that ensured the permanence of the currency.

This finding helps explain why historical interpretations focused exclusively on military action fail to capture a fundamental aspect of Roman expansion. Conquering a territory was only the beginning. For it to be effectively integrated into the Republic, markets, cities, administrative institutions, religious centers, and permanent networks of exchange had to be built. The maps of currency circulation are beginning to reveal this process of integration.

Another important conclusion concerns the evolution of Roman economic geography itself. “In the early periods analyzed, coins remained relatively close to the places where they had been minted. However, as the Republic expanded its borders, they began to be found at increasingly greater distances. In statistical models, this appears as a progressive reduction in the effect of distance on coin circulation. In other words, regions previously separated by geographical barriers became progressively integrated through a common network of transportation, markets, and institutions,” Haddad explains.

According to the researcher, this is perhaps one of the most significant findings of the study. “As territorial expansion occurs, we begin to find coins at increasingly greater distances. The role of distance gradually diminishes, suggesting a growing integration of the territory,” he summarizes. This conclusion goes far beyond numismatics [the discipline dedicated to the study of coins as historical documents]. It suggests that the circulation of coins can serve as an indirect indicator of the degree of economic integration among the empire’s different regions.

Diversified markets

Spatial analysis revealed the intensity of monetary circulation and different functional regions within the Roman Republic.

“At the center of the system was the city of Rome itself, where expenditures related to public administration predominated. Surrounding it was a highly integrated economic core corresponding to the Italian Peninsula, where monetary circulation primarily reflected market activities. Further out lay an intermediate belt, a sort of buffer zone between the consolidated core and the recently incorporated regions. Within it, administrative, economic, and military expenditures coexisted. In the areas of most recent expansion, however, expenditures related to conquest and territorial occupation predominated. As those regions were pacified and permanently incorporated into the Roman world, the share of military expenditures decreased, giving way to the growth of civil, administrative, and commercial activities,” Haddad explains.