The word tunnel began life far from the earth. In medieval France, a tonel was a small barrel or a barrel-shaped net strung across a clearing to catch partridges. The connection to underground passages came through architecture: early mine shafts and urban underpasses were built with barrel-vault ceilings, and the resemblance was close enough to carry the name with it. The underlying root, Medieval Latin tunna, referred to a large cask and may trace back to a Celtic word for a hollowed vessel, though this remains debated. English adopted the net sense first in the fifteenth century, and within a hundred years the architectural meaning had overtaken it entirely. By the time Brunel began boring beneath the Thames in the 1820s, nobody remembered the partridge nets at all.