A version of this story appeared in Science, Vol 378, Issue 6623.Download PDF
On a Sabbath Saturday in March 1349, the Jewish community of Erfurt was wiped out in a pogrom. The archbishop of Mainz, who had granted Jews the right to live and work in the medieval German city, tried the pogrom’s ringleaders, local merchants and city council members who owed money to Jewish money lenders. One was executed and the rest exiled. The city’s Christian population, meanwhile, was forced to pay restitution.
Five years later, a new Jewish community took root in the narrow, winding streets. Beginning in 1354, the city funded new houses and a synagogue, drawing Jews from across Europe to Erfurt. “That must have convinced them it would never happen again,” says Karin Sczech, an archaeologist who works for the city.
For 100 years, Erfurt’s Jews flourished. They bathed in a ritual bath, or mikvah, on the banks of the Gera River and buried their dead in a large cemetery just outside the city walls. Then it all came to an end, again. In 1454, the town council revoked the rights of Erfurt’s Jewish population, forcing them to leave town. The city built a granary on top of their cemetery, destroying hundreds of graves and repurposing Jewish tombstones to build its stout stone walls.
On a sunny fall day, Sczech points out a 192-square-meter plot she and a team of other archaeologists excavated on the former cemetery’s grounds a decade ago. With a municipal construction project about to start on the site, their goal was to save, study, and rebury any human remains uncovered by the building work. The local Jewish community was closely involved, and “their wish was to do as little excavation as possible,” Sczech says.
A meter or two under the ground, in the shadow of the 500-year-old granary, the team found the remains of more than 60 people, almost all of them oriented with their legs pointed east—toward Jerusalem. Their skeletons were well-preserved, along with traces of wooden coffins and nails.
Before the remains were reburied last year at a nearby cemetery, they yielded a gift: DNA that is shedding light on the origins of the Ashkenazim, the major Jewish population that emerged in Germany in the Middle Ages and later expanded into central and Eastern Europe. Together with a smaller scale study published in September that looked at DNA from six individuals from the Middle Ages unearthed in Norwich, England, the Erfurt analysis offers clues to where the Ashkenazim came from centuries earlier, and what happened along the way. The studies also confirm other evidence that today’s Ashkenazi Jewish population, which numbers more than 10 million people spread around the world, has roots in a band of no more than a few hundred who survived a population bottleneck in Europe more than 1000 years ago.
The Erfurt study, which appears today in Cell, is the first major study of a medieval Jewish population from a genetic perspective. “We just got a really nice angle from genetic resources that we didn’t have before,” says Elisheva Baumgarten, a historian at the Hebrew University of Jerusalem who was not involved with the study. “The cumulative evidence can tell us more than history alone—that to me is the really exciting part.”
Perhaps equally important, the archaeological effort was made possible by a rabbinical ruling that may establish a precedent for future studies of ancient Jewish remains that yield precious insights without violating religious sensibilities.
ARCHAEOLOGISTS HAVE UNCOVERED evidence of Jewish communities in Germanic provinces of the Roman Empire as early as the 300s C.E., particularly in what is today the city of Cologne. During the medieval period, a trio of German cities—Worms, Mainz, and Speyer—was known as the cradle of Ashkenazi culture, with records of Jewish life going back to about 900 C.E.
But the period in between largely remains a mystery. Were the Jews of Erfurt and other medieval cities tenacious holdovers from the Roman era, as some have proposed? Or were they the descendants of more recent pioneers who crossed the Alps around 800 C.E. to found tight-knit communities along the Rhine, near modern-day Frankfurt? “Ashkenazi Jews emerge in the Rhineland as migrants,” says Leonard Rutgers, a historian at Utrecht University and a co-author on the Cell paper. “But if they came from elsewhere, where did they come from?”
To find out, geneticists have tried to work backward from modern DNA. Today’s Ashkenazi populations have high rates of certain genetic diseases because many individuals carry identical mutations, increasing the risks to their offspring. Those mutations, along with other shared DNA sequences, are clues to an early population bottleneck that drastically reduced Jewish genetic diversity. “Whether they’re from Israel or New York, the Ashkenazi population today is homogenous genetically,” says Hebrew University geneticist Shai Carmi.
Some ultra-Orthodox Ashkenazi communities today regularly administer genetic compatibility tests during matchmaking to limit the risk that children will inherit genetic diseases, and pre-conception testing is common in other Ashkenazim. But even though modern Ashkenazi genomes have been closely scrutinized, they can’t give a clear picture of events 1000 or more years ago. “It helps to have data from the past,” Carmi says.
In 2017, Carmi met with Harvard University geneticist David Reich at his lab. Reich—an expert on ancient DNA whose research has been criticized in the past for not engaging meaningfully enough with the concerns of local communities—encouraged him to pursue ancient DNA sampling, if he could find an ethical way to do it. Speaking from his Boston-area home on the morning of Rosh Hashana, the Jewish New Year, Reich said that although he is of Jewish descent, before Carmi reached out he had avoided studying Ashkenazi genetics. “It’s hard to study one’s own community,” he says. “Working on oneself is complicated—you have biases towards what the results would be that are cognitively difficult.”
Carmi left that initial meeting feeling pessimistic about studying DNA from ancient Jews. “I thought this would be impossible,” he says, “because there would be no permission to sample.” Searching for ancient DNA for analysis would mean grinding up tiny bits of bone for sequencing. Destructive sampling would also be needed for radiocarbon dating. “It’s a hard rule in Judaism that you don’t disturb the dead,” says Alexander Nachama, chief rabbi of the Jewish Community of Thuringia and head of the modern-day Jewish community in Erfurt.
Carmi pressed ahead, contacting historians and archaeologists in Europe to see whether suitable samples existed. “The historians thought I was crazy,” Carmi says. But a few got back to him—including Sczech, who had received rabbinical permission to measure bones from the Erfurt cemetery to determine their sex and ages at death, techniques that don’t harm the skeletal material.
Carmi also reached out to an Orthodox rabbi in Israel. After studying centuries-old interpretations of Jewish law and listening to Carmi’s explanation of the science, the rabbi suggested a workaround: teeth. Because they fall out naturally (“They’re deciduous, like the leaves of a tree,” Reich says), the rabbi concluded that stray teeth are not part of the body in the same way as a skull or rib. Researchers couldn’t go looking for them, but if loose teeth turned up—as part of a rescue excavation, for example—they could be sampled without violating Jewish beliefs.
With a rabbinical ruling in hand, Carmi approached Jewish authorities in Germany, including the chief rabbi of Erfurt at the time. They were hesitant. “They didn’t want to be the first to allow an ancient DNA study or go against an established ruling,” Carmi says. The Israeli rabbi’s reasoning ultimately won over Erfurt’s Jewish community, and Carmi was able to sample the loose teeth of 38 individuals from the cemetery before the bodies were reburied in a 2021 ceremony.
For colleagues working on Jewish sites elsewhere in Europe, the ruling represents a religiously acceptable way to apply scientific techniques to date Jewish remains and study their ancestry and diet. Carmi says it might even be applied to DNA analyses of mass graves from World War II. “The use of teeth seems to me to be an excellent compromise,” says Philippe Blanchard, an archaeologist working for France’s National Institute of Preventive Archaeological Research who was not involved with the study. “I hope that the results of this first study will show what is at stake and what benefits each side—scientists and the Orthodox—can expect.”
NO SIMILAR DISCUSSIONS of religious ethics preceded the Norwich study, because it was only after an initial analysis in 2011 that the researchers realized the 17 people whose remains were found during construction work might have been Jews killed in a pogrom. The presence of DNA sequences also found in Ashkenazi Jews today was one clue. “When we first tested the DNA, we got just a few hundred base pairs,” says Ian Barnes, an evolutionary geneticist at London’s Natural History Museum who worked on the study. “The best I could say was they were compatible with Jewish origin.”
The bones were reburied in 2013 in a multidenominational ceremony. Five years later, the local Jewish community asked to move them to a quieter spot. Before they were reburied a second time, the authors secured permission to analyze them again, this time yielding higher resolution results that definitively linked them to modern Ashkenazi populations. Subsequent radiocarbon dating, meanwhile, showed the bones were about 800 years old, placing them around the same time as an 1190 massacre of the town’s Jews, which took place on the eve of the First Crusade. “The minute you get dates, it seems reasonable it could be this one antisemitic event,” Barnes says. “Put together, everything helped to build the case.”
The DNA results from Norwich and Erfurt both confirm that modern Ashkenazim are descended from a small founding population. Based on modern Jewish DNA, some researchers had speculated this founder group emerged from a population crunch in the 13th and 14th centuries, when the religious fervor of the Crusades and false accusations that Jews spread the Black Death sparked violent pogroms. But the new data point to a different scenario that played out earlier.
“We already see clear evidence for that bottleneck” in the 14th century teeth from Erfurt, Carmi says. Disease mutations and long stretches of identical genetic code in the medieval DNA implied the bottleneck occurred centuries earlier. One type of mitochondrial genetic material—DNA that is passed through the maternal line—was identical in one-third of the people in the excavated plot, evidence that they all descended from a single woman who probably lived 500 to 1000 years earlier.
In the Norwich individuals—which DNA shows included three sisters and a young boy with red hair and blue eyes—geneticists found the same disease markers seen in modern Ashkenazi populations, at about the same frequencies. “That tells you the bottleneck happened prior to these individuals dying in 1190,” Barnes says. “This is a clear example of how powerful these data are.”
At the same time, small differences among the dozens of Erfurt genomes suggested medieval Ashkenazi communities weren’t completely homogeneous, despite the earlier bottleneck. In the city archives, co-author Maike Lämmerhirt of the University of Erfurt found clues to that diversity in tax and property records. Some of the names of 14th century Jewish residents—Salman of Würzburg, Abraham of Rothenburg—suggest family roots in Bavaria, south and west of Erfurt. Other prominent Erfurt Jews, such as Baruch of Pilsen or Jacob of Bohemia, apparently traced their ancestry far to the east, in one case as far away as modern-day Kaliningrad, now in Russia, or beyond.
That mixture of east and west “is exactly what we get from the genetic results,” Sczech says: After first branching out from a single, small founding population into small communities across Europe, including medieval Great Britain, the medieval Ashkenazim apparently mixed back together in places like Erfurt generations later.
Isotopic signals in the teeth supported the DNA evidence. Tooth enamel captures the isotopic mixture of the water where a person grew up, and in the Erfurt cemetery the analysis showed parents with distant birthplaces—probably in Eastern Europe—were buried near their children, who grew up locally. “That’s a hint that we have the founders,” Sczech says. “It’s the first time ever we have all these results coming together.”
By comparing the Erfurt genomes with modern and ancient DNA data from many different populations, the researchers were able to peer even further back, to the origins of those scattered European communities. The comparisons suggested the Ashkenazi circa 1350 had a mix of ancestry resembling populations from southern Italy or Sicily today, with components found in modern Eastern Europe and the Middle East mixed in. “That fits the historical data,” says Krishna Veeramah, a geneticist at Stony Brook University who was not involved in the work.
One traditional tale about Ashkenazi roots may not be far from the truth: A family or small group of Jews arrived in Germany around 800 C.E., crossing the Alps at the invitation of Charlemagne, the first Holy Roman emperor, and settled in the Rhineland.
BEYOND A LOOK at population dynamics, the Erfurt results offer a window into medieval Jewish culture. Although genetic variations show the postpogrom community drew its members from across Europe, their burials are all similar, reflecting common traditions. “They were all considered Ashkenazi Jews,” Carmi says.
The genetic similarity between the Erfurt community and modern Ashkenazim 600 years later was also telling. “These people lived about 25 generations ago, and an intermarriage rate with outsiders of more than one in 500 per generation would have shifted Ashkenazi ancestry by an amount we could detect,” Reich says. “But that didn’t happen. That’s new information.”
The Jewish community’s central position in medieval European life makes its genetic isolation even more remarkable. The role of Jews as bankers, craftspeople, traders, and money lenders would have put them in constant contact with their Christian neighbors. In Erfurt, as in many medieval cities, synagogues, ritual baths, and Jewish houses were in the heart of town, right next to the city hall and at the intersection of two major roads. Archival records show Jews and Christians went into business together and Christians served as wet-nurses to Jewish children. “Jews and Christians were constantly in each others’ lives. But it looks like they didn’t have children together,” Baumgarten says. “We as modern people don’t have the words to describe that complex sense of belonging.”
Today Erfurt’s Jews are at the center of the city once more, as part of an effort to make its ancient synagogue and mikvah a UNESCO World Heritage Site dedicated to Jewish daily life in the Middle Ages. It’s a story Baumgarten says is often overshadowed by the horrors of the Holocaust and the pogroms that punctuated centuries of coexistence. “To make it only into a dark story would be a mistake for European culture at large,” she says. “The truth is the Jews of medieval Germany settled there by invitation, were welcomed there when they came and were integrated into medieval German space—and all the while were a religious, and sometimes persecuted, other.”
Now their genomes are proving central to the story of all Ashkenazim–including its formative event, the bottleneck that so dramatically marked the DNA of millions of people living today. Though these new studies help pin down its timing, no one knows what caused it. Bottlenecks call to mind catastrophes, such as massacres or discrimination that prevents people from marrying outside their community. “It’s fair to say Jewish history is one big sequence of bottlenecks,” Rutgers says.
But to Reich, the Erfurt data suggest a brighter possibility: that long before the Erfurt Jews were laid to rest, somewhere in Europe a few dozen people flourished, passing their genes and culture to millions of people living today despite a history of brutal persecution. “Perhaps it’s the legacy of a small town that had a tradition of very large families, or maybe a few towns with very strong founder events,” Reich says. “Bottlenecks are often thought of as a crisis, but sometimes it’s a group that’s been incredibly successful.”
Correction, 1 December, 9:55 a.m.: An earlier version of this story misstated Philippe Blanchard’s name.
