The roundhouse is a type of house with a circular plan, built in western Europe before the Roman occupation. The wall was made either of stone or of wooden posts joined by wattle-and-daub panels, and the roof was conical and thatched.

Most of what is assumed about these structures is derived from the layout of the post-holes, although a few timbers have been found preserved in bogs. The rest has been filled in by experimental archaeology, which has shown the most likely form and function of the buildings. For example, experiments have shown that a conical roof with a pitch of about 45 degrees would have been the strongest design. It has also been shown that, although a fire would have been lit inside for heating and cooking, there could not have been a smoke hole in the apex of the roof, for this would have caused an updraught that would have rapidly set fire to the thatch. Instead, smoke would have accumulated harmlessly inside the roof space, and slowly leaked out through the thatch.

Many modern simulations of roundhouses have been built, for example at:

• Butser Ancient Farm, Hampshire, England
• Bodrifty Iron Age Settlement, Cornwall, England
• Flag Fen near Peterborough, England
• Tatton Iron Age roundhouse and pit, Cheshire, England