Mullion

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A mullion is the element that forms a division between units of a window or screen, or is used decoratively. When dividing adjacent window units its primary purpose is a rigid support to the glazing of the window. Its secondary purpose is to provide structural support to the horizontal lintel above the window opening (Horizontal elements separating the head of a door from a window above are called transoms). In the case of multiple arched windows combined building a bifora (or trifora, etc), the equally shaped windows might be coupled by mullions (instead of a column with base and capital), framed by a blind arch or the mullions dissolving in Gothic tracery.

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