Iron Age skeletons found under bridge may have been hit by a tsunami

Twenty people may have died 2000 years ago when an Iron Age bridge suddenly collapsed following a tsunami or flood, but scientists also cannot rule out that they were sacrificed

Skulls found in the bank of river Thielle, in Switzerland, are now stored in a museum in Hauterive
(Credit: Schweizerischer Nationalfonds / Fonds national suisse)

For decades, scientists have wondered about the history of 20 people, as well as a handful of farm animals, who seemingly drowned 2000 years in a Swiss river. One idea is that these individuals were sacrificed from a bridge, which later collapsed. But new evidence supports the notion that, for at least some of them, their demise – along with the bridge’s – was due to a natural disaster.

In 1965, archaeologists uncovered objects including wood and bones from a 750-square-metre site in the banks of the river Thielle in Cornaux/Les Sauges in western Switzerland. The wood had once formed a bridge built in about 135 BC that was repaired twice, 20 and 30 years later, according to analyses of its beams, says Zita Laffranchi at the University of Bern in Switzerland.

Those archaeologists uncovered multiple male skeletons in similar positions, often pinned under beams. For many experts, the findings fit with previous nearby discoveries related to Iron Age sacrificial rituals, which often took place around water.

But others thought the evidence pointed to a huge wave or other force of nature causing the sudden collapse of the bridge. That makes sense given the region’s history of floods and lake tsunamis, possibly spurred by earthquakes, says Marco Milella, also at the University of Bern.

Now, renewed investigations suggest that the deceased received massive blows from blunt objects, such as from the bridge as it crashed into the water, says Laffranchi. But they also indicate that the deaths spanned two centuries, leaving unanswered questions about what killed some of these people prior to the bridge’s collapse, she says.

As part of these investigations, Laffranchi, Milella and their colleagues analysed the skeletons and wood, stored at the Laténium Museum in Hauterive.

DNA sequencing showed that none of the people – made up of 17 adults, one adolescent and two children – appeared to be related, says Milella. Most were young men, which supports the sacrifice idea, as natural disasters tend to affect a more even distribution of the sexes and a variety of ages, including families, the researchers write in their paper.

All the deceased, including the animals, sustained violent blunt trauma leading to fractures from head to toe, none of which showed signs of being intentional, says Milella. The fact that the skeletons were entangled with the beams suggests they may have got swooped up in the bridge’s collapse, he says.

But radiocarbon dating revealed death dates ranging from about the 3rd to the 1st centuries BC. This challenges the idea that the bridge collapse was solely responsible, because not all of the deceased could have died in the same incident, says Milella. This could mean that some were tied to beams and sacrificed from the bridge, he says. It is also possible that the bridge fell several times over the years, especially given its history of repairs, he says.

This study reflects the importance of “layering as many lines of data as possible” to learn how ancient populations lived and died, says Madeleine Mant at the University of Toronto in Canada. “It is certainly possible that a terrible accident is at the heart of this story.”


Journal reference:

Scientific Reports DOI: 10.1038/s41598-024-62524-y