Must Farm

Must Farm is a Late Bronze Age settlement near Whittlesey, east of Peterborough in Cambridgeshire, England. Around 850 BCE a group of timber roundhouses built on stilts over a slow-moving river caught fire and collapsed into the water. Silt sealed the charred structures, preserving posts, walls, roofs and household contents. The Cambridge Archaeological Unit excavated the site in 2015-16 in a £1.1 million project funded by Historic England and the building-products company Forterra, and the full results were published in 2024 in two reports by the McDonald Institute for Archaeological Research.

The settlement

• Structures: four large roundhouses and a square entrance structure were uncovered. About half the original settlement was destroyed by 20th-century quarrying, so it was probably about twice as large.
• Stilts: buildings stood about 2 m (6.6 ft) above the river, with walkways linking some houses, inside a 2 m high fence of sharpened posts.
• Size: the largest roundhouse had almost 50 m² (540 sq ft) of floor space; roundhouse one was about 8 m (26 ft) across.
• Lifespan: unseasoned timber shows the village was built less than a year before it burned. Remains of young lambs suggest the fire happened in late summer or early autumn.
• Population: up to about 60 people in family units.

The roofs

Must Farm gives unusually complete evidence of a prehistoric British roof.

• Frame: rafters met at an apex over the centre of each house and probably overhung the walls as short eaves. They rested on a ring of large split timbers at the top of the wall, carried on posts. The wall plates have mortise joints; the rafters do not. Rafters were closely spaced, so purlins may not have been needed. Many fell in a fan pattern onto the channel floor.
• Covering: the final reports describe a roof of three layers: straw for insulation, then turf, then clay on top. During excavation the team noted large quantities of burnt turf, often containing charred cereal roots, indicating it was cut from cultivated ground.
• Clay: deposits of mostly unburnt clay, roughly a tonne per house, clustered around the central posts. One theory is that clay packed around the rafters at the apex shielded them from fire, possibly forming part of a smoke outlet; this would explain why apex rafters survived unburnt while the eave ends were heavily charred.

The weight of turf and clay implies carefully engineered stilts and a stout frame.

Significance for roofing history

Many earlier reconstructions of British roundhouses assumed a covering of reed or straw thatch alone. The evidence of a layered roof with turf and clay over straw shows that roundhouse roofs could be heavier and more fire-resistant than many reconstructions assume. The site gives a rare physical check on assumptions about covering and smoke venting used in other roundhouse reconstructions.