![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/5/58/10_Downing_Street._MOD_45155532_%2528cropped%2529.jpg/640px-10_Downing_Street._MOD_45155532_%2528cropped%2529.jpg&w=640&q=50)
Transom (architecture)
Horizontal structural piece separating a door from a window above it / From Wikipedia, the free encyclopedia
For other uses, see Transom (disambiguation).
In architecture, a transom is a transverse horizontal structural beam or bar, or a crosspiece separating a door from a window above it. This contrasts with a mullion, a vertical structural member.[1] Transom or transom window is also the customary U.S. word used for a transom light, the window over this crosspiece.[1][2] In Britain, the transom light is usually referred to as a fanlight, often with a semi-circular shape, especially when the window is segmented like the slats of a folding hand fan. A prominent example of this is at the main entrance of 10 Downing Street, the official residence of the British prime minister.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/5/58/10_Downing_Street._MOD_45155532_%28cropped%29.jpg/640px-10_Downing_Street._MOD_45155532_%28cropped%29.jpg)