Four Million Ancient Coins Show How Rome Built an Integrated Economy

For centuries, the story of Rome’s rise was told through the words of classical authors, the inscriptions carved into stone, and the ruins scattered across three continents. In recent years, however, a quieter transformation has been reshaping how historians and archaeologists reconstruct the ancient world. Vast archaeological collections are being digitized, standardized, and made publicly available, and quantitative methods originally developed for entirely different purposes are being applied to millions of scattered records. Archaeology and history, like biology and astronomy before them, have entered the era of data science, and the results are beginning to challenge long-standing assumptions about how the ancient economy actually worked.

A striking example of this new approach comes from the University of São Paulo in Brazil, where two economists have reconstructed the monetary circulation of the Roman Republic using the remains of approximately four million coins unearthed in excavations conducted over the past two centuries. Focusing on the period from 155 BCE to 2 CE, Eduardo Amaral Haddad of the School of Economics, Business, and Accounting and Inácio Fernandes Araújo of the Luiz de Queiroz College of Agriculture combined techniques from regional economics, spatial analysis, and geographic information systems with large international archaeological databases. Their study, published in the journal Humanities and Social Sciences Communications, part of the Nature group, arrives at a provocative conclusion: the consolidation of Roman rule depended less on military conquest than on the economic integration of the territories that conquest brought under Roman control.

The logic of the method rests on a simple but powerful observation. Every coin preserved by archaeology carries three pieces of information: where it was minted, when it was produced, and where it was found roughly two thousand years later. Taken individually, each record says very little. But when millions of records are analyzed together, patterns emerge that no single artifact could reveal. The paths taken by money, the intensity of economic exchange between regions, the degree of integration across the Mediterranean, and even the institutional evolution of one of antiquity’s largest economies all leave traces in the aggregate distribution of coinage. In effect, the researchers treated coin hoards not as collections of curiosities but as data points describing the economic relationships that structured the Roman Republic.

The project had unlikely origins. In 2014, Haddad was on sabbatical at Princeton University, working on mainstream economics questions, when he began attending a weekly seminar in the Department of Classical Studies out of personal interest. At one meeting, he watched a presentation that used shipwreck remains and pottery shards to reconstruct trade networks in the ancient Mediterranean. The idea stayed with him. Shortly afterward, while exploring the university library, he found a catalog of Roman coins containing exactly the information he needed: minting dates, production locations, and excavation sites. He photocopied the catalog, reasoning that the same tools economists use to study flows of people, goods, and income between modern cities could be turned on the Roman Mediterranean. What began as a hobby eventually became a long-term research program, deepened by a distance-learning graduate course on the ancient Mediterranean at the University of Leicester in the United Kingdom.

Carrying out the analysis required solving a problem that had frustrated earlier attempts at large-scale reconstruction: fragmentation. Information on Roman coins was long scattered across museums, libraries, private collections, and researchers’ archives, making systematic study nearly impossible. That changed as institutions such as the American Numismatic Society began coordinating international projects to digitize and standardize these collections under common recording protocols. The main source for the study was Coin Hoards of the Roman Republic Online, a database dedicated to hoards from the Republican period. The researchers also drew on ORBIS, a Stanford University platform that simulates travel along the roads, rivers, and sea routes of the Roman world and estimates the time and cost of journeys between hundreds of locations, as well as the Pleiades gazetteer and the Roman Road Network database, which provided georeferenced information on cities, roads, and ports across the ancient Mediterranean.

After careful curation, the team assembled a dataset of roughly four million coins organized into 24,646 hoards, corresponding to 5,167 distinct pairs of minting and discovery sites. Rather than analyzing individual coins, whose numbers are distorted by differences in preservation, loss, and reuse over the centuries, the researchers worked at the level of these archaeological records. Their first question was deceptively simple: was the spatial distribution of the coins random, or did it follow a pattern? Statistical tests drawn from regional economics and economic geography gave an unambiguous answer. The coin finds clustered in ways that were far from chance, concentrating along the main trade routes of the Roman world. Cross-referencing the coin distributions with the road network revealed something even more striking: a clear spread of coinage radiating outward from the city of Rome itself, following the infrastructure the Republic had built.

Tracing the money was only the first step. To understand why some regions saw intense monetary circulation while others remained peripheral, the researchers needed to model the Roman economy itself. They organized information from the historical and archaeological literature into a framework inspired by social accounting matrices, a tool normally used to analyze contemporary economies. The model describes the relationships among the principal economic actors of the time, including the government, households, landowners, merchants, slaves, and the army, and represents the flows of goods and payments linking them. It also distinguishes between types of production and consumption, from food and raw materials to manufactured goods and luxury items, the latter capable of traveling far greater distances. The model also captured a gradual but profound transformation: the progressive monetization of the Roman economy, as payments for supplying the army, maintaining slaves, and funding public activities shifted from payment in kind to payment in coin, a shift visible in the archaeological record itself.

It was at this point that one of the study’s most consequential findings emerged. A widely held interpretation assigns the Roman army the dominant role in spreading currency through conquered territories, on the intuitive logic that advancing legions carried soldiers who received wages and suppliers who traded goods. The results only partially confirm this. Military structures were decisive in the initial phase of expansion, introducing monetary circulation into newly conquered lands. But their influence waned as territories were permanently incorporated. Currency took root only once those regions developed economic, religious, administrative, and civic structures capable of generating a lasting demand for money. The army, in other words, acted as a catalyst that opened regions to monetization, but it was the economy that made the currency permanent. This helps explain why interpretations focused exclusively on military action miss a fundamental dimension of Roman expansion: conquest was only the beginning, and genuine integration required markets, cities, institutions, religious centers, and enduring networks of exchange.

The study also documents the evolution of Roman economic geography over time. In the earliest periods analyzed, coins tended to remain relatively close to where they were minted. As the Republic expanded, coins began appearing at ever greater distances from their points of origin, and in the statistical models this appears as a progressive weakening of the effect of distance on circulation. Regions once separated by geographic barriers were being stitched together through a common network of transportation, markets, and institutions. The researchers describe this as perhaps the most significant finding of the study, because it suggests that coin circulation can serve as an indirect indicator of economic integration across the ancient world. The spatial analysis further revealed a set of nested functional regions: at the center, the city of Rome, dominated by public administration; around it, a highly integrated economic core in the Italian Peninsula, where circulation reflected market activity; beyond that, an intermediate belt where administrative, economic, and military expenditures coexisted; and, at the frontier, zones of recent expansion where conquest-related spending predominated until pacification allowed civil and commercial activity to take hold. Together, these findings recast the spread of a common currency as the connective tissue of an empire in the making.

Subject of Research: Mapping coin circulation and economic networks in the Roman Republic using digital archaeology and spatial analysis

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

Article References: Traces of nearly four million coins reveal how Rome achieved economic integration. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Roman Republic, coin hoards, economic integration, digital archaeology, spatial analysis, numismatics, monetization, regional economics, ancient Mediterranean, trade networks, ORBIS, social accounting matrices