What Are Mullioned Windows? Unveiling the Charm of Architectural Elegance

Mullioned windows, characterized by their distinctive vertical bars known as mullions, are a hallmark of architectural elegance with roots in Gothic design. These windows not only enhance structural support but also add aesthetic charm to buildings, a feature particularly prominent in historic cathedrals and period homes. Mullions have been utilized since the medieval period, as noted by the University of Kent, which states that their use peaked during the 14th century, reflecting the era's architectural innovation. Understanding what mullioned windows are is essential for appreciating their blend of function and form, which continues to influence modern architecture and restoration projects.

Originally, mullions were structural elements which helped to support the weight of the building around them, in addition to breaking up a window into several panes of glass, which made it less expensive to install. Glass used to be a very costly construction material, and the use of large sheets of glass was uncommon because the biggest panes of glass were used to make mirrors. In addition, construction techniques did not always allow for a huge unsupported opening in a building, making huge glass windows impossible as well as expensive.

Modern mullioned windows may use nonstructural mullions made from a variety of materials, although stone is the classic choice. Wood, metal, and plaster can all be used to create mullions, which may also be made decorative with fanciful painting or carving. If a window is divided horizontally as well as vertically, these horizontal dividers are called transoms.

It is not uncommon to see stained glass installed in mullion windows. Larger mullioned windows may be used to illustrate a brief story or allegory, especially in church architecture. In this sense, the windows are more decorative than functional, since the stained glass obscures the flow of light into the building. The mullion design may also be used on doors, and stone mullions are sometimes installed without glass to ventilate a space such as an enclosed courtyard while still creating a sense of security and privacy.

It is important to distinguish between mullioned windows and windows which are divided into a grid of panes by muntins, sometimes called glazing bars. Mullioned windows often have unusual shapes, and they are frequently arched at the top. Gridded windows are square or rectangular, and the grid is regular, with evenly spaced panes of glass divided into a grid, rather than large blocks of glass divided by mullions or transoms. This grid design is common in sash windows, popular features in Western architecture.

We know that mullioned windows were used in the great Gothic cathedrals of Europe. However, plenty of examples exist well before Gothic architecture became a thing in the 12th century. You'll also find them in Islamic architecture, starting before the 10th century.

Many buildings in the Middle Eastern world include a mashrabiya, a projecting self-contained oriel window that’s with latticework intricately carved into the wood. Some versions contain stained glass. Their primary purpose was more than ornamental. Thanks to their passive cooling, they could help route cooler air into the building. Jars and basins of water were sometimes placed inside a mashrabiya to increase the cooling effect.

The origins of mashrabiyas can be traced back to Egypt’s old Coptic churches. Well before these churches were even built, ancient Egyptians used a similar type of woodworking for the doors and roofs of their homes. Documentation of Coptic woodworking on Islamic buildings exists from the Tulunid Dynasty, which encompassed Egypt and Syria during the ninth and 10th centuries. The lattice woodwork was an appealing feature for another reason: It afforded a bit of privacy for people inside the building.

It’s common to see both intricate latticework and mullions on windows throughout the Middle East. Some mullioned windows in Gothic architecture feature similarly intricate designs. These are traceries, detailed pieces of open stonework set in the windows’ upper halves. Traceries are one easily recognizable element of Gothic architecture.

You may be surprised to learn how Gothic architecture got its name. Believe it or not, “Gothic” was used as an insult during Renaissance times. Back then, the term “Goths” didn’t refer to members of the post-punk subcultures we know today. They were a Germanic tribal civilization that lived around the Vistula River in what is now modern-day Poland. When you hear about the Goths sacking Rome in 410 C.E., we’re talking about those folks — specifically, the Visigoths led by King Alaric I.

Long after their civilizations ended, Gothic people were seen as barbarians. You can thank Italian writer Giorgio Vasari, who disparagingly called the distinctive building style “Gothic” during the 1530s. However, Gothic architecture has nothing to do with the Goths who invaded Rome. It actually developed out of Romanesque architecture, which dominated Europe between the 10th and 12th centuries. Romanesque builds were influenced by Byzantium and ancient Roman buildings and exhibited key features like semi-circular arches, thick walls, barrel vaults, and large towers. Maria Laach Abbey in Germany is a notable example of Romanesque architecture.

Gothic architecture saw its heyday between the 12th and 16th centuries. Buildings constructed during that time tend to have rib vaults, flying buttresses, and pointed arches. Elaborate stained glass windows also became a hallmark of this style. And of course, some of those are mullioned windows.

Of course, stained glass was reserved for elaborate builds. You’re more likely to see them in French Gothic constructions like the Chartres Cathedral and the Basilica of Saint-Denis near Paris. The Chartres Cathedral has a few mullioned stained-glass windows — for instance, the North Rose Window depicting Mary, Jesus, and several prominent Old Testament figures.

The North Rose Window is an excellent example of how Gothic builders combined several features into a single construction. It’s a rose window, a common feature seen in many other buildings of the period. So named their shape and visual features, rose windows can either have mullions or traceries. Not all rose windows have stained glass. But the Chartres Cathedral has three of them, including the South and West Rose Windows.

Both the North and South Rose Windows combine a rose window at their tops above a set of mullioned windows at the bottom. Each of these windows looks like a cohesive unit, thanks to the skillful construction of their creators. Their stone traceries and mullions are best viewed from the outside, but the stained glass designs show their full glory when seen from the inside.

Like many architectural innovations adopted during the Middle Ages, mullioned windows are perfect examples of how style and function can easily coexist in the same feature. Gothic buildings, especially the legendary cathedrals, tended to be much taller than their predecessors. Mullions lent extra support inside the windows in which they were housed. The same holds for flying buttresses, rib vaults, and other characteristics of Gothic architecture. Together, these elements created an unmistakable style that still inspires many of us today.