Mullion

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,...