Ancient Balkan genomes reveal how Slavic Europe was formed

Iñigo Olalde, Ikerbasque Research Fellow at the UPV/EHU and Ramón y Cajal Researcher has, together with the Institute of Evolutionary Biology (IBE: CSIC-UPF) and Harvard University, led a study in which they have, for the first time, reconstructed the genomic history of the first millennium of the Balkan Peninsula. To do so, the team recovered and analysed the ancient genome of 146 individuals who inhabited present-day Croatia and Serbia during that period. The work, published in the prestigious journal Cell, depicts the Balkans as a global, cosmopolitan frontier of the Roman Empire and reconstructs the arrival of Slavic peoples in this region. 

For the first time, the team has identified three individuals of African origin who lived in the Balkans under Rome's imperial rule. Furthermore, the research establishes that the migration of Slavic peoples from the 6th century onwards represented one of the biggest permanent demographic changes in the whole of Europe, the cultural influence of which continues to this day. 

The Roman Empire transformed the Balkans into a global region  

First the Roman Republic and then the Roman Empire incorporated the Balkans and turned this border region into a crossroads of communications and a melting pot of cultures. This is confirmed by the study which reveals that immigrants from far away were attracted to the region by the economic vitality of the empire. 

Through the analysis of ancient DNA, the team was able to identify that, during Roman rule in the region, there was a large demographic influx from the Anatolian Peninsula (located in modern-day Turkey) that left a genetic imprint on the Balkan populations. Yet no trace of Italic ancestry has been observed in the genomes analysed. “These populations that had come from the East were fully integrated into the local Balkan society. At Viminacium, for example (one of the main cities of the Romans, located in present-day Serbia), we found an exceptionally rich sarcophagus in which a man of local descent and a woman of Anatolian descent had been buried,” said the lead author of the article Íñigo Olalde, Ikerbasque Research Fellow in the BIOMICs group at the UPV/EHU and research associate at Harvard University (he had previously been a "La Caixa Junior Leader" researcher in the IBE's Palaeogenomics group). 

The team also revealed the sporadic long-distance mobility of three individuals of African descent to the Balkan Peninsula while under imperial rule. One of them was a teenager, whose genetic origins are to be found in the region of present-day Sudan, beyond the boundaries of the ancient Empire. “The isotopic analysis of the roots of his teeth revealed that in his childhood he had a seafood diet very different from that of the rest of the individuals analysed,” said Carles Lalueza-Fox, senior researcher at the Institute of Evolutionary Biology (IBE) and director of the Museum of Natural Sciences of Barcelona (MCNB). 

What is more, he had been buried with an oil lamp representing an iconography of the eagle, which is related to Jupiter, one of the most important gods for the Romans. Lalueza-Fox pointed out that “archaeological analysis of his grave reveals that he may have been part of the Roman military forces, so we would be talking about an immigrant who had travelled from a long way away to the Balkans in the 2nd century CE”. “This indicates to us a diverse, cosmopolitan Roman Empire, which embraced populations from far beyond the European continent.”  

The Roman Empire welcomed barbarian populations long before its fall 

The study identified a number of individuals of northern European and steppe ancestry who inhabited the Balkan Peninsula during the 3rd century at the height of the Roman occupation. Anthropological analysis of their skulls reveals that some of them were artificially deformed, a custom peculiar to certain populations of the steppes and the Huns, often referred to as “barbarians”. 

These findings support historical and archaeological research and point to the presence of individuals from outside the borders of the Empire, beyond the Danube, long before the fall of the Western Empire. “The borders of the Empire were much more diffuse than the borders of today's nation states. The Danube served as a geographical boundary of the Empire but acted as a communication route and was highly permeable to the movement of people,” said Pablo Carrión, IBE researcher and co-lead author of the study. 

Slavic populations altered the demographics of the Balkan region 

Following the fall of the Western Roman Empire, and in particular from the 6th century onwards, the study reveals the large-scale arrival in the Balkans of individuals genetically similar to the modern Slavic-speaking populations of Eastern Europe. Their genetic footprint represents between 30% and 60% of the ancestry of today's Balkan peoples, which constitutes one of the largest permanent demographic shifts anywhere in Europe during the period of the Great Migrations. 

Although the study detects the sporadic arrival of individuals from Eastern Europe during earlier periods, it is from the 6th century onwards that a strong migratory surge can be observed. “According to our ancient DNA analysis, this arrival of Slavic-speaking populations in the Balkans took place across several generations and involved entire family groups including both men and women,” explained Carrión. 

The study also identifies that the establishment of Slavic populations in the Balkans was bigger in the north, with a genetic contribution of 50-60% in present-day Serbia, and gradually smaller towards the south, with a genetic representation of 30-40% in mainland Greece and up to 20% in the Aegean islands. “Their genetic legacy is visible not only in today's Balkan Slavic-speaking populations, but also in other groups that include regions where Slavic languages are not currently spoken, such as Romania and Greece,” said David Reich, a researcher at Harvard University in whose lab the recovery and sequencing of the ancient DNA was carried out. 

Coordination and cooperation to rewrite Balkan history 

The 1991 war in Yugoslavia led to the separation of the Balkan peoples into the various countries that currently make up the region, and its consequences persist to this day. However, researchers from across the region have collaborated on the study. “Croatian and Serbian researchers have been collaborating on the study. This is a great example of cooperation, given the recent history of the Balkan Peninsula. At the same time, this type of work is an example of how objective genomic data can contribute towards leaving behind social and political problems linked to collective identities that have been based on epic narratives of the past,” said Lalueza-Fox. 

The team developed a de novo genetic database of the Serbian population in order to reconstruct the history of the Balkans. “We were faced with the situation in which there was no genomic database of the current Serbian population. In order to construct it and use it as a comparative reference in this study, we had to look for people who called themselves Serbs on the basis of certain shared cultural traits, even if they lived in other countries such as Montenegro or North Macedonia,” said Miodrag Grbic, lecturer at the University of Western Ontario and visiting lecturer at the University of La Rioja. 

Despite the question of identity, marked by the more recent history of the Balkans, the genomes of the Croatians and Serbians analysed speak of a heritage shared in equal measure between Slavic and Mediterranean populations. 

As Lalueza-Fox pointed out, “we believe that, together with archaeological data and historical records, the analysis of ancient DNA can contribute towards the reconstruction of the history of the Balkan peoples and the formation of the so-called Slavic peoples of southern Europe.” 

“The image that emerges is not one of division, but of a shared history. The Iron Age people inhabiting the Balkan region were similarly affected by migrations during the time of the Roman Empire and by Slavic migrations later on. Together, these influences gave rise to the genetic profile of the modern Balkans, regardless of national borders,” concluded Grbic.  

Additional information 

The study was led by the Institute of Evolutionary Biology (IBE), a joint centre of the Spanish National Research Council (CSIC) and the Pompeu Fabra University (UPF), and Harvard University, with the participation of the UPV/EHU, the University of Western Ontario and the University of La Rioja (UR).