European soldiers and civilians poured into the Levant in the 12th and 13th centuries, often killing or displacing local Muslim populations and establishing their own settlements in an effort to seize control of sites sacred to three major religious groups.

But in a new study, DNA from the skeletons of nine soldiers hints that the armies of the Crusades were more diverse and more closely linked with local people in Lebanon than historians previously assumed. The genetic evidence suggests that the Crusaders also recruited from among local populations, and European soldiers sometimes married local women and raised children, some of whom may have grown up to fight in later campaigns.

Living and dying side by side

For centuries, the mingled, charred bones of at least 25 soldiers lay buried in two mass graves near the ruins of the Castle of St. Louis, a 12th- to 13th-century Crusader stronghold near Sidon, in south Lebanon. Several of the skeletons (all apparently male) bore the marks of violent death, and the artifacts mingled with the bones—buckles of medieval European design, along with a coin minted in Italy in 1245 to commemorate the Crusades—mark the pit's occupants as dead Crusader soldiers, burned and buried in the aftermath of a battle. From nine of them, geneticist Marc Haber and his colleagues at the Wellcome Sanger Institute obtained usable DNA sequences, which offer a rare look into the ranks of the soldiers who fought on one side of the 200-year series of wars.

Before becoming the namesake of the largest metro area in Missouri, French King Louis IX led the Seventh Crusade, a final (and ultimately failed) push by European forces to wrest control of Syria and Lebanon from Muslim rulers based in Egypt. In 1253, Louis' forces suffered a major defeat at Sidon, and the king himself arrived on the scene a few days after the battle. Accounts from the time describe Louis personally piling soldiers' decomposing remains into mass graves in the aftermath. Whether he really did that is unclear, of course. But it's reasonably likely—based on the date of the coin and radiocarbon dating of material from the pits—that these skeletons could be the remains of some of those men.

“We see this exceptional genetic diversity in the Near East during medieval times.”

It appears the soldiers were a more diverse group than many historians supposed. When Haber and his colleagues compared the DNA sequences to databases of modern DNA samples from around the world, three of the dead Crusaders closely resembled modern Europeans: two were most likely of Spanish ancestry, and one was most likely Sardinian. Four of the Crusaders' genomes closely resembled those of modern Lebanese people and DNA samples from the bones of people who lived in Lebanon under the Roman Empire around 2,000 years ago. That suggests local people had joined the Crusades, which lines up well with historical accounts of local Christians becoming soldiers, officers, and knights in the Crusader forces.

"It wasn't just Europeans," Haber said in a statement to the press. "We see this exceptional genetic diversity in the Near East during medieval times, with Europeans, Near Easterners, and mixed individuals fighting in the Crusades and living and dying side by side."

Metropolitan Museum of Art

Sarah Collins 2011

Sarah Collins 2011

Sarah Collins 2011

Sarah Collins 2011

Claude Doumet-Serhal

Generations of fighting

If you used statistical analysis to group the most similar genomes together (which is exactly what Haber and his colleagues did), the three European soldiers would cluster together in one group, and the four Lebanese soldiers would form another. But the other two soldiers would fall somewhere in the middle, which suggests that they may have been the children of Europeans and Near Eastern people.

To get more information about the two soldiers' ancestry, Haber and his colleagues looked at DNA sequences from their Y chromosomes. Because that particular set of DNA is usually passed directly from father to son, it's possible to trace paternal lineages through Y-chromosome DNA the same way that maternal lineages can be traced through mitochondrial DNA. The three Europeans' Y-chromosome DNA fell into groups of lineages usually associated with European ancestry. So did the two soldiers with mixed ancestry. Mitochondrial DNA, which passes only from mother to child, was less clear: the two soldiers' mitochondrial genomes both fell into a group that's common all over Europe and the Near East.

That seems to suggest that these two soldiers both had European fathers and Near Eastern mothers, but it's also possible that their parents came from mixed ancestries themselves; there's no way to say for sure based on the DNA evidence. Either way, it underscores how long the Crusades lasted. It's one thing to say that the Crusades were a 200-year series of conflicts, but it's another to realize that a wave of European migrants to the Levant intermarried with local people. Their children—and perhaps their children's children—apparently grew up to fight in the next round of warfare.

Ghosts of the past

But although hundreds of thousands of Europeans fought and settled in the Levant from 1095 to 1291, there's no trace of European ancestry in the genomes of the people living in Lebanon today. In fact, Haber and his colleagues compared the genomes of modern Lebanese people with DNA extracted from the bones of people who lived near Mt. Lebanon between 237 and 632 CE, when the area was part of the Roman Empire. It turned out that they hadn't changed very much. Today's Lebanese people are clearly descended from the people who have lived in the area since the Bronze Age, with little trace of the temporary European invaders.

"If you look at the genetics of people who lived during the Roman period and the genetics of people who are living today, you would think that there was just this continuity," Haber said in a statement. "You would miss that, for a certain period of time, the population of Lebanon included Europeans and people with mixed ancestry."

Haber and his colleagues suggest that the interaction between groups during the Crusades didn't last long enough or happen at a large enough scale to leave a genetic trace 800 years later. The genetic traces of such brief encounters, they say, tend to get diluted over time. That suggests that, while looking at modern people's genomes can reveal some things about our large-scale shared human story, many events may go missing. That's why looking at ancient DNA from the remains of people who lived closer in time to these events can tell us things that modern DNA can't. And that can help fill in gaps in written history.

The American Journal of Human Genetics, 2019. DOI: 10.1016/10.1016/j.ajhg.2019.03.015 (About DOIs).