Building a roundhouse

'Roundhouse' is the name given by archaeologists to a type of circular building that was especially common in Iron Age Britain, around 2000 to 2500 years ago.

Roundhouses ranged in size from less than 5m in diameter to over 15m. The life-size example reconstructed in 2002 by the Museum of London was at the small end of the scale. Some roundhouses may have been used as workshops or to store food supplies, others as homes or even shrines. Under Heathrow Airport and at Uphall Camp, Ilford, archaeologists have discovered complete Iron Age villages composed almost entirely of roundhouses.

Unfortunately, roundhouses were built almost entirely of perishable materials such as wood, straw, clay and turf, so very little survives for archaeologists to find. Very often, the only thing left is a shallow, circular ditch that tells us a lot about the size and position of the building but rather less about how it was constructed.

In the bottom of the ditch there are sometimes holes at regular intervals. These will have been made by upright posts, driven in to form a frame for the walls. In other cases, archaeologists find an inner ring of pits for the wall posts, suggesting that the ditch functioned simply as a drainage channel for water running off the roof.

Recent London digs have produced some interesting detailed evidence for the construction and appearance of roundhouses. On a site in Cheapside there survived part of the wattle and daub infill between the wall posts, and at 10 Gresham Street at least one building had a hearth in the centre of it.

We can use three main sources of evidence:

• Evidence from archaeology: From the size of the post holes, for example, we can work out the thickness of the original posts, indicating their possible height and strength.
• Evidence from circular buildings constructed in more recent times in Africa and elsewhere in the world: These are often similar in size to the Iron Age British buildings. Typically, they have woven wattle walls that stand vertically to around shoulder height. A steep conical roof, made from thatch or mud, sits either on top of the wattle walling or on a special horizontal beam. Some archaeologists, however, believe that Iron Age houses were constructed something like an upside-down basket and so looked more like an igloo.
• Evidence from reconstruction: However much effort you put into reconstructing a building on paper, there is nothing like trying to build a 'real' one if you want to know if it works. Through reconstruction we have learned how steep the roof has to be if it is not to collapse; how much ventilation is needed for a fire; and what it is like to live in the house during cold weather.

Roundhouses have now been discovered on at least three sites near the Museum. The interesting thing is that they all belong to the same short period of around ten years, very early in the life of Roman London (AD 50-60) - not to the pre-Roman Iron Age period.

We believe that the Roman soldiers and officials settled mainly on the eastern side of what is now the City of London - roughly between the Bank of England and the Tower of London. Here they put up large buildings in typical rectangular Roman style. On the western side of the City, nearer the Museum and south of where the Guildhall now stands, it seems that native Britons came to trade with the Romans and built a town in their traditional style - with roundhouses.

On the 10 Gresham Street site, several roundhouses were built in this period, alongside two small rectangular buildings. In one of the roundhouses, people had been making beads that looked like native British beads but in fact were made from recycled Roman glass. This shows that the old and the new cultures co-existed for some time. The entire roundhouse settlement closed down in about AD60. However, none of the buildings showed any sign of fire damage. This is surprising, because in most parts of Londinium we find thick layers of debris - evidence of how the city was totally burned down by Boudica in AD 61-2. Did Boudica's followers let the roundhouses escape destruction because Britons were living there? Or were they protected simply by their position some way back from the main centre of the town?

Francis Grew
Department of Early London History and Collections
October 2002

On the internet...

Fact pack on the building of a roundhouse in the Museum garden

Other replica roundhouses that you can visit...

Castell Henllys, near Newport, Wales
Flag Fen, near Peterborough
Butser Ancient Farm, near Petersfield, Sussex