Mullion, in architecture, a slender vertical division between adjacent lights or subdivisions in a window or between windows in a group. Mullions appear with the invention of tracery and are particularly characteristic of Gothic architecture and early Renaissance architecture in northern and western Europe.
A mullionis a vertical elementthat forms a division between units of a window or screen, or is used decoratively. When dividing adjacent windowunits its primary purpose is a rigid support to the glazing of the window.
A Moorish mullioned window in the Alhambra of Granada. Stone mullions were used in Armenian, Saxon and Islamic architecture prior to the 10th century. They became a common and fashionable architectural feature across Europe in Romanesque architecture, with paired windows divided by a mullion, set beneath a single arch.
The vertical members, called mullions, are attached to the building at every floor and are spaced 1.5 to three metres (five to 10 feet) apart; the horizontal members, called muntins, are attached between the mullions. The rectangles between the grid of mullions and muntins are filled with transparent or….