mullion

thumb|upright|A mullioned window in the church of San Francesco (Lodi)|San Francesco of [[Lodi, Lombardy]] A mullion is the vertical 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.

==History== Stone mullions were used in Armenian, Saxon and Islamic architecture prior to the 10th century. They became a common architectural feature across Europe in early Mediaeval and Romanesque architecture, with biforas, paired windows divided by a column or a mullion, set beneath a single arch. The same structural form was used for open arcades as well as windows, and is found in galleries, porticos and cloisters.