Henges (like Avebury) and hillforts (like Maiden Castle) are probably two of the most iconic features of the British landscape. These impressive ancient monuments are nearly as big as they are old, but can you tell them apart? Here’s how to spot which is which.

When DigVentures started their investigations at Oldbury Camp in Gloucestershire (a rare lowland hillfort locally known as ‘The Toot’), I may have been heard to quietly whisper ‘I think it might be a henge, not a hillfort’.

This probably seems like a strange thing to say. Surely two completely different types of ancient monument, with two thousand years between them, should be very easy for archaeologists to tell apart? Well, things aren’t always that easy, and sometimes it’s fun to question the accepted wisdom.

What even IS a henge?

Avebury, Wiltshire, is a great example of a henge.

A henge is a type of circular monument that people built during the late Neolithic period, about 5,000 – 4,300 years ago. Typically, they consist of a huge artificial soil bank (or ‘earthwork’) with a deep ditch, enclosing a roughly circular space.

The thing that really defines a henge, though, is that their ditch is almost always on the inside of the bank. Clearly, this makes absolutely no sense from a defensive point of view – if you were trying to stop people attacking the monument you would put the ditch outside the bank.

Inside the monument can be any number of things – stone circles, timber circles and other structures, and archaeologists usually think of them as spaces for ceremonies, rituals and gatherings.

Avebury in Wiltshire is a great example of a henge where an enormous ditch and bank surrounds a large stone circle, which itself contains two smaller stone circles and a double timber circle.

Right, so we’ve got henges sorted. But what’s a hillfort?

Maiden Castle, Dorset, is a mighty example of a hillfort.

A hillfort is another type of earthwork monument that people built during the late Bronze Age or Iron Age period (1000 BC – AD 43). They’re often found on hilltops, with one or more lines of earthworks enclosing a roughly circular or oval space, with elaborate entrances.

They’re found across Britain, Ireland and Europe too, but unlike henges, these earthworks always have their ditch outside the bank, putting any attackers at a distinct disadvantage if they try and get in.

Archaeologists often evidence that people lived inside them, with roundhouses and pits or structures for storing grain. Maiden Castle in Dorset is a really huge example of a hillfort that was surrounded by multiple lines of banks and ditches.

Here’s why archaeologists sometimes get them mixed up

Bank on the inside equals henge, on the outside equals hillfort. Seems like a simple enough rule to follow, so how could anyone get them mixed up?

Confusingly, some of most famous henges don’t actually conform to the rule about the ditch and the bank, including the most famous of them all: Stonehenge.

Henges that look like hillforts

Stonehenge actually has two banks with a ditch in between. And similar sites like Llandegai in Gwynedd also have a ditch outside the bank. These fall into a category of early henges built in about 3000 BC sometimes called ‘proto-henges’ by archaeologists.

So just because a monument doesn’t follow the rule, it doesn’t automatically remove the possibility it is a prehistoric henge. And some monuments that do follow the rule are often still thought to be Iron Age.

Hillforts that look like henges

Take Wolstonbury Hill in Sussex for example. This is an enclosure with a ditch on the inside and a bank on the outside, but was thought to be an Iron Age hillfort for many years.

New dating evidence has shown the main enclosure to be probably late Bronze Age. It has two earlier phases, the earliest of which may be Neolithic. Perhaps this was a Neolithic henge that was later occupied by people in the late Bronze Age?

Henges that were turned into hillforts

Re-using, re-building or adapting monuments actually happens quite often in the ancient past. What starts out as an early Neolithic causeway-ed enclosure (another type of earthwork monument!) might later become a Bronze Age enclosure, which then gets re-developed into a full-blown Iron Age hillfort.

This is exactly what happened at Maiden Castle, as well as at The Trundle in Sussex and Hembury Hill in Devon. It’s only by careful excavation that these different phases can be teased out.

It’s what’s inside that counts

Ok, I hear you sigh, they might have confusingly similar earthworks, but surely it’s what inside that counts. If there are stone circles and ‘ritual’ activity it’s a henge; if it’s a settlement then it’s a hillfort, right? Wrong.

Recent excavations at henges like Durrington Walls and Marden Henge, both in Wiltshire, have found evidence of small houses, feasting remains and occupation, suggesting that people were living within these enclosures (or crucially, immediately before these enclosures were constructed) for at least some of the time.

Hillforts weren’t really forts anyway

And the latest thinking on hillforts is that they weren’t necessarily permanent settlements or built entirely for defence. The dramatic and impressive ramparts might have been more about impressing other people, creating community identity and cohesion, and displaying the wealth and power of a group, rather than real defence. Some hillforts never seem to have been occupied and others appear to have shrines or special buildings within them.

Finally, what about where they are? The clue is in the name – hillforts are on hills, henges are in lower lying positions. But once again, things aren’t quite so clear-cut.

Many hillforts, including Oldbury Camp, are in unusual low-lying locations. These are often sometimes referred to as ‘marsh-forts’ but are poorly understood. And some henges are positioned in quite dramatic upland locations with extensive views, such as Cairnpapple Hill in West Lothian.

So is Oldbury-on-Severn a henge or a hillfort?

So why did I think that Oldbury Camp might be a henge? Its low-lying position is unusual for a hillfort, but its location near a river is entirely typical for a henge. The entirely circular shape is more like a henge than a hillfort.

The general sparsity of artefactual evidence suggests that there probably wasn’t much Iron Age settlement activity going on, leaving the site quite ‘clean’. And it wouldn’t have been impossible for the earthworks to have been Neolithic in date.

That’s why the excavations at Oldbury Camp are so exciting – we’re really trying to find out something about this site that hasn’t received much attention before: when, how and why was it built?

So, while the general consensus is that Oldbury Camp is some kind of lowland hillfort, I’m going to play devil’s advocate.

Of course, I’m entirely happy to be proved wrong when we find that it is an entirely Iron Age marsh-fort, but it’s still possible that its origins were older than that. Only careful archaeological excavation and analysis will give the answer, and we’re all very anxious to see what the dating evidence suggests when the results come back from the lab

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Sue Greaney

Sue Greaney

Sue is an archaeologist with a passion for British prehistory. She works at English Heritage and is a PhD candidate at Cardiff University, studying Neolithic ceremonial monument complexes. She also likes long-distance walks, travelling to remote places and drinking real ale.

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