A mullion is a vertical element that forms a division between units of a window or screen, or is used decoratively. It is also often used as a division between double doors. 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 an arch or lintel above the window opening. Horizontal elements separating the head of a door from a window above are called transoms.

History

Stone mullions were used in Armenian,

Saxon The Saxons ( la, Saxones, german: Sachsen, ang, Seaxan, osx, Sahson, nds, Sassen, nl, Saksen) were a group of Germanic * * * * peoples whose name was given in the early Middle Ages to a large country ( Old Saxony, la, Saxonia) near the No ...

and

Islamic architecture Islamic architecture comprises the architectural styles of buildings associated with Islam. It encompasses both secular and religious styles from the early history of Islam to the present day. The Islamic world encompasses a wide geographic ...

prior to the 10th century. They became a common and fashionable architectural feature across Europe in

Romanesque architecture Romanesque architecture is an architectural style of medieval Europe characterized by semi-circular arches. There is no consensus for the beginning date of the Romanesque style, with proposals ranging from the 6th to the 11th century, this lat ...

, with paired windows divided by 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 and cloisters. In

Gothic architecture Gothic architecture (or pointed architecture) is an architectural style that was prevalent in Europe from the late 12th to the 16th century, during the High and Late Middle Ages, surviving into the 17th and 18th centuries in some areas. I ...

windows became larger and arrangements of multiple mullions and openings were used, both for structure and ornament. This is particularly the case in Gothic cathedrals and churches where stained glass was set in lead and ferramenta between the stone mullions. Mullioned windows of a simpler form continued to be u