What does extrados mean?
The extrados is the outermost curved surface of an architectural arch — the exterior boundary of the arc, as opposed to the intrados, which is the inner curve visible beneath it. The term belongs chiefly to the vocabulary of architecture, structural engineering, and building history, where precision about an arch's geometry matters: loads travel through the masonry between the intrados and the extrados, and designers often need to specify the thickness of that curved band. In practice one might speak of dressing stones 'along the extrados' of a vault or reinforcing the extrados of an old brick bridge. Though specialized, the word is a useful marker of technical literacy in discussions of historic structures, and its pairing with intrados makes the pair easy to remember once encountered.
nounThe outer curved surface of an arch, especially the upper exterior edge of a masonry arch as distinct from its inner curve.
- The outer curved surface or upper boundary of an arch, viewed from outside the structure.
"The stonemasons dressed the blocks carefully along the extrados so the arch's outer face would sit flush with the wall."
"The engineer calculated the thrust line to ensure it stayed within the ring between the intrados and the extrados."
"Weathering over the centuries had eroded the voussoirs along the bridge's extrados."
The regular English plural is 'extradoses'; because each arch has one extrados, the plural appears mainly when discussing multiple arches.
"The surveyors measured the extradoses of all five bridge spans."
Every arch has two faces — and while everyone admires the inner curve you walk under, architects give equal attention to its hidden twin on the outside, called the extrados.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of extrados
Extrados comes from French, formed from Latin 'extra', meaning 'outside' or 'beyond', combined with 'dos', meaning 'back' — literally the 'outer back' of the arch. It entered English during the eighteenth century as architectural writing adopted French technical vocabulary. It shares its Latin prefix with words such as 'extraordinary' and 'extraneous', and stands as the natural counterpart to 'intrados'.
How extrados is actually used
A technical term used almost exclusively in architecture, civil engineering, and the history of construction; rare in general conversation. It is typically used in the singular when referring to a single arch's outer curve.
Easily confused with extrados
The intrados is the inner, lower curve of an arch (the soffit), while the extrados is the outer, upper curve.