Ancient Rome was the capital city of an empire that encompassed some 70 million inhabitants. An international research team now reports on data from a genetic study suggesting that, just as all roads may once have led to Rome, in ancient times, a great many European genetic lineages also converged in the ancient city. Results from the research present possibly the most detailed analysis to date of genetic variability in the region. They reveal a dynamic population history from the Mesolithic era (~10,000 BCE) into modern times, which spans the rise and fall of the Roman Empire.

“This study shows how dynamic the past really is,” said Hannah Moots, a graduate student in anthropology at Stanford University, who is co-lead author of the published paper, which is reported in Science, and titled, “Ancient Rome: A genetic crossroads of Europe and the Mediterranean.” Moots added, “In Rome we’re seeing people come from all over, in ways that correspond with historical political events.” The study was headed by the Stanford University team in collaboration with the University of Vienna and Sapienza University of Rome.

Go back to the 8th century before the common era (BCE), and Rome was one of many city-states on the Italian Peninsula, the authors wrote. But in less than 1,000 years Rome grew into the largest urban center of the ancient world. “Rome controlled territory on three continents, spanning the entirety of the Mediterranean—or Mare Nostrum, ‘our sea,’ as the Romans called it.”

At its zenith the ancient Roman Empire spanned three continents, and tens of millions of people across Europe, the Near East, and North Africa. At the Empire’s center was Rome, the first city to reach more than one million residents in the ancient world. Rome remained unrivaled in Europe until the industrial revolution nearly 1,500 years later. But even long before the rise of Imperial Rome, the region represented an important cultural crossroads between Europe and the Mediterranean.

Given its historical importance, the Roman empire has been studied extensively, but far less is known about the genetic lineages of Rome’s inhabitants through the ages, the investigators pointed out. To help provide some new insights into the genetic makeup of the region’s population “throughout the trajectory of the empire,” they turned to modern genetic techniques, which over the last decade or so have been used increasingly to study DNA sampled from ancient skeletons. Rome presented an ideal opportunity to use the same DNA analysis techniques to fill in ancestral details left out of the historical record. “The historical and archaeological records tell us a great deal about political history and contacts of different kinds with different places—trade and slavery, for example—but those records provide limited information about the genetic makeup of the population,” said Jonathan Pritchard, PhD, a professor of genetics and biology at Stanford University, and one of the paper’s senior authors.

To understand the genetic makeup of these ancient people, the Stanford team partnered with European researchers, including senior authors Alfredo Coppa, PhD, a professor of physical anthropology at Sapienza University, and Ron Pinhasi, PhD, an associate professor of evolutionary anthropology at the University of Vienna, to gather 127 human DNA samples from 29 sites in and around Rome, dating from the Stone Age to medieval times. The timeline spanned nearly 12,000 years of Roman prehistory and history. Their analysis of the ancient DNA allowed the team to place genetic changes in what they call “the context of a rich archaeological and historical record.”

An increasing number of studies have used DNA sampled from ancient skeletons to fill in important details of human history. In a new study, Stanford researchers and their European colleagues drew on ancient DNA to construct the first genetic history of Rome.

The individuals sequenced fell into three distinct genetic clusters. “Mesolithic hunter-gatherers; early farmers (Neolithic and Copper Age individuals); and a broad historic cluster encompassing individuals from the Iron Age to the present,” the investigators wrote. “The oldest genomes in our dataset are from three Mesolithic hunter-gatherers (10,000 to 7,000 BCE) from Grotta Continenza, a cave in the Apennine Mountains.” Putting the DNA analyses in context with timelines highlighted at least two major migrations into Rome, as well as several smaller but still significant population shifts over just the last few thousand years, according to Pritchard, who is also a member of Stanford Bio-X. The findings indicated that as the Roman Empire expanded around the Mediterranean Sea, immigrants from the Near East, Europe, and North Africa migrated into Rome. This significantly changed the face of the ancient world’s great city, Pritchard suggested.

An analysis of some of the earliest samples is in basic agreement with what has been found around Europe—and demonstrating an influx of farmers primarily descended from early agriculturalists from Turkey and Iran around 8,000 years ago, followed by a shift toward ancestry from the Ukrainian steppe somewhere between 5,000 and 3,000 years ago. “The first major ancestry shift in the time series occurred between 7,000 and 6,000 BCE, coinciding with the transition to farming and introduction of domesticates including wheat, barley, pulses, sheep, and cattle into Italy,” the scientists noted. “The second major ancestry shift occurred in the Bronze Age, between ~2,900 and 900 BCE … During this period, major technological developments increased the mobility of populations.” It was a period during which people had developed overland transport methods, including chariots and wagons, while advances in sailing technologies also “facilitated easier and more frequent navigation across the Mediterranean.” By the founding of Rome, traditionally dated to 753 BCE, the city’s population had grown in diversity and resembled modern European and Mediterranean peoples.

Rome began as a humble city-state, the authors suggested. “Although there is no direct historical or genetic information about the origins of Rome, archaeological evidence suggests that in the early Iron Age, it was a small city-state, among many culturally and politically similar Etruscan and Latin neighbors. However, within 800 years Rome had gained control over an empire that extended to the west as far as Britain, south into North Africa, and east into Syria, Jordan, and Iraq. Archaeological evidence and contemporary accounts indicate that as the empire expanded there were connections between Rome and other areas in its domain, through trade, military campaigns, slavery, and transport routes. While this was borne out by the genetic evidence, the results also indicated that there was a huge shift in the ancestry of people who lived in Rome, but that this ancestry was primarily from the Eastern Mediterranean and Near East.

The next few centuries appear somewhat turbulent. The empire split in two, diseases ravaged the Roman population, and the city was invaded more than once. Those events left their mark on the city’s residents, who shifted towards a western European ancestry. Later, the rise and reign of the Holy Roman Empire brought an influx of central and northern European ancestry. “During the Imperial period … the most prominent trend is an ancestry shift toward the eastern Mediterranean and with very few individuals of primarily western European ancestry,” the team noted. “One possible explanation for the predominance of gene flow from the east into Rome is the higher population density in the eastern Mediterranean than the west.”

The ancient world was thus perpetually in flux, both in terms of culture and ancestry. “It was surprising to us how rapidly the population ancestry shifted, over timescales of just a few centuries, reflecting Rome’s shifting political alliances over time,” Pritchard said. “Another striking aspect was how cosmopolitan the population of Rome was, starting more than 2,000 years ago and continuing through the rise and dissolution of the empire. Even in antiquity, Rome was a melting pot of different cultures.”

“… within each time period, individuals exhibited highly diverse ancestries, including those from the Near East, Europe, and North Africa,” the authors stated. “These
high levels of ancestry diversity began prior to the founding of Rome and continued through the rise and fall of the empire, demonstrating Rome’s position as a genetic crossroads of peoples from Europe and the Mediterranean.”

The researchers hope to be able to expand the geographic range of ancient DNA they can sample. That would allow them to say with more certainty how ancient populations mixed and moved around. Over the longer term, they also hope to add new study parameters. For example, the group plans to look at the evolution of traits such as height, lactose tolerance, and resistance to diseases such as malaria, which may have changed over time.

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