Roman Frog Feast or Death Ditch: What Really Left Thousands of Frog Bones in a Mysterious English Gully?

I am a zooarchaeologist; my expertise lies in macrofauna, so when I come across things like mice, lizards, and shrews, I usually set them aside for someone else to analyze because they are microfauna. Most sites I analyze have surprisingly few microfauna. The ones that do often comprise various shrew species, and the occasional snake. Something neither I nor any of my zooarchaeology friends have come across is frogs. I know for a fact they occur at other sites and across southern Africa (I even had a massive bullfrog sitting in my garden once), but none of our assemblages ever have them.

However, on the other side of the world, a few years ago, quite the opposite was discovered. During excavations for the National Highways A14 Cambridge to Huntingdon Road Improvement Scheme near Cambridge, archaeologists found over twelve thousand microfauna remains. Most of these bones came from amphibians, though they also found vole, mouse, snake, shrew, and lizard remains. They were discovered throughout Settlement 5, an Iron Age/Roman site, but an unusually large number (over 9,000 bones) came from a single shallow gully.

The media took to the story like flies to honey. Speculation ran rampant, from Iron Age people feasting on thousands of frogs to a mass frog tragedy culminating in a frog death pit.

Four years later, archaeologists have been hard at work trying to figure out what really happened here. They discovered this was no mass Roman feast of frogs, nor did thousands of unlucky amphibians fall into a pit and die. They did not freeze during winter hibernation, nor had they come to feast on the remains of grains left by the settlement inhabitants.

So, what really happened to these frogs, and how did so many of them end up in a gully inside a human settlement?

Life on the Edge of the Fens

Settlement 5 lies in a valley that drains into the Great Ouse, on the edge of the Fens. The Fens are a flat, low-lying bit of land where even the slightest shift in sea level, climate and geology reshapes the landscape. During the Iron Age, a single silt and shingle bar across the Wash, a shallow bay on the east coast into which multiple rivers drain, kept the sea at bay. However, it also prevented rivers from draining properly, leading to multiple marshes, peat bogs, and shallow lakes further inland.

This meant that people living inland built their settlements on higher ground, safe from winter floods, including Settlement 5.

After the Middle Iron Age, people started clearing the surrounding woodlands to make way for grazing pastures. They built various enclosures, including Enclosure 11, with a shallow gully in its center. The gully's exact function is unknown.

By the Roman period, the climate had improved, sea levels fell, and the Fens were transformed. Waters retreated, leaving behind temporary ponds that dried up one by one. The heart of the Fens remained wet, becoming a rich source of fish, waterfowl, reeds, and summer grazing pastures.

Meanwhile, the temporary ponds became the perfect breeding grounds for frogs, possibly triggering a series of frog booms.

Around the same time, people remodeled Settlement 5 into a planned grid. But the area where Enclosure 11 once sat was largely left alone. Perhaps because people could still see its remains or because they remembered it had once been there and left it alone out of respect.

Reading the Bones

Fast forward many centuries, and archaeologists came upon Enclosure 11 and its mysterious gully. Overall, the researchers recovered 12,683 microfauna remains, 9,135 of which came from the gully.

Microfauna can tell you a lot about a site's history. If people left them there, they can reveal human food and ritual behavior. Natural deaths are useful too, such as those caused by freezing, disease, flooding, landslides, and the like. Microfauna can reflect past local environments and tell you whether a period was wetter, drier, colder, or warmer.

But first, you need to figure out how the microfauna were deposited. If humans deposited the remains, you might expect signs of burning, cut marks, charring, or a preference for hind legs (after all, if you order frogs at a restaurant, they don't usually serve you the head, arms, or body, do they?).

But what if something else deposited them?

Years ago, I volunteered at a bird-of-prey rehabilitation center. My job was quite simple: every morning at 5 AM, I had to go feed the birds. Not too bad, except it was about 5 degrees, and I was handling half-frozen chicken chicks. Some birds of prey were smaller than others, so they only got half a chick (I distinctly remember ripping one of the chicks in half and yolk coming out of it… yum). One rule I had to follow was to check whether the birds had regurgitated a pellet before feeding them.

Birds of prey regurgitate things they cannot digest, such as bones, feathers, fur, and teeth. If I fed them before they regurgitated their pellets, this could cause a blockage. So I would look for the oval-shaped, usually yellowish, sticky pellets and throw them away before feeding the bird.

But how do you tell whether a bone was regurgitated by something in an archaeological assemblage?

Digestive acids. Well, not the acids themselves, but rather the marks they leave behind. When a bone is digested, it becomes rounded and smoothed. For predators, the level of digestion and breakage can tell you what predator was the most likely culprit. Some animals digest bone so thoroughly you're left with basically nothing but a weirdly deformed, undiagnostic fragment of bone; others are milder, leaving bones nearly untouched.

Death By Owl

The researchers looked at a subsample of 1,711 specimens; they found that most came from the Common Frog, with about 85.9% of amphibian bones having been digested. They showed no signs of cut marks or burn marks, so this was no Roman feast, nor was the shallow gully a natural trap into which the frogs accidentally fell.

The level of digestion and signs of breakage suggested most of these bones were deposited by owls, specifically short-eared owls. A few Hen harriers may also have contributed bones, as they often roost together.

Based on radiocarbon dates from three bones, one from each section of the gully, the frogs died around the 3rd century AD.

Interestingly, frog humeri can tell you how old a frog was when it died. Most of these frogs died in the autumn or winter of their first year, suggesting the owls accumulated them during a single year's frog boom.

What likely happened was that as the temporary shallow ponds dried up, the frog populations followed. Basically, imagine the water table dropping: it creates a shallow pond. Frogs breed in that pond. The water level drops some more; the pond dries up, but farther away another shallow pond emerges, and the frogs breed there. Then the water level drops again, the pond dries, a new pond forms down the line, and so on. The frog boom thus follows the ponds. These frogs may have resulted from the Fens' water level lowering, creating a series of shallow ponds and frog booms.

But there's still one more question then. Some owls, in particular short-eared owls, are incredibly shy. They avoid places with people and dogs nearby, such as a settlement. Yet Enclosure 11 was right inside a settlement. Why roost there?

The authors suggest the area may have been a livestock route used only in summer, meaning the owls would have been largely undisturbed in winter, when the frog boom occurred. It's also possible the Romans deliberately avoided the area, perhaps out of respect or because of some ritual significance.

Either way, we now know the thousands of microfaunal bones were not the result of a Roman feast or frog ritual. Nor did the frogs accidentally fall into the gully. Owls, not people, caused the remains through a feeding frenzy.

Funnily enough, they also give us evidence of absence. You've heard the familiar phrase, "absence of evidence isn't always evidence of absence". Well, in this case, the evidence (feeding remains of owls) suggests the absence of people, literally evidence of absence.

Microfauna is rarely examined in archaeological samples, despite the wealth of knowledge it can provide. They are often seen as helpful in reconstructing past environments and not much else. But here at Enclosure 11 in an Iron Age/Roman settlement, they provided much more. Yes, they gave some insight into the environment, but they also showed us how people used, or in this case avoided, parts of their own settlement.

Why do you think people largely avoided Enclosure 11?

Let me know what you think, and if you'd like to support this blog and the person writing it, you can chip in once, monthly, or yearly. Only if you'd like to.

References

Clarkson, P., Ewens, V., Scholma-Mason, O., Hambleton, E., Andrews, P., & Jenkins, E. (2026). An Owl’s Eye View: Human–Animal Entanglement at the Roman Fen Edge. Environmental Archaeology, 1–24. https://doi.org/10.1080/14614103.2026.2746302