The west European Neolithic is famed for its funerary and ceremonial monuments, but the evidence for houses is sparse. Can this be explained by the materials of which they were built? On the northern coast of Brittany, the site of Lillemer rises from the surrounding marshes and presents abundant evidence of Middle Neolithic occupation, contemporary with the passage graves of the region. Surprisingly, their evidence includes the remains of collapsed earthen-walled structures, providing the northernmost example of this type of architecture in a Neolithic context and a possible explanation for the invisibility of much Neolithic domestic architecture.