Diocletian Windows: Definition, Architecture & Style

Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Of the many kinds of windows you can use, how many would make you feel like a Roman emperor? In this lesson, we'll check out Diocletian windows and explore their unique history.

Diocletian Windows

Imagine that you're hoping to re-stabilize the Roman Empire by dividing its territories among four emperors, and you really just want your home to say that about you. Well, you're in luck. Anybody who wants to emulate the life of the Roman emperor Diocletian can now have his windows.

Of course, for those of us not looking to conquer the Mediterranean, Diocletian windows are still a great choice. Diocletian windows are semicircular, arch-shaped windows or openings that are generally segmented into thirds with two prominent mullions (vertical dividers). It's a classic look, one that was even good enough for emperors.

Diocletian window in a Venetian church
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History of the Diocletian Window

Okay, maybe we should start with a brief history lesson here. Diocletian was a Roman emperor of the late 3rd and early 4th centuries CE. He did a lot during his reign, but all we need to know in this lesson is that he shared the throne with a co-emperor named Maximian. To honor his partner in the empire, Maximian commissioned the largest baths of imperial Rome and named them the Baths of Diocletian. They were completed in 306 CE.

One of the notable architectural features of the Baths of Diocletian was a set of very large upper-story windows. These windows were shaped as a semicircular arch, and segmented with two large, brick mullions. This was the inspiration for the modern Diocletian window, which emulates the windows of the Baths of Diocletian. Because the Latin word for baths was thermae, some modern architects also call these thermal windows.

Neoclassical Diocletian Windows

So, how did this architectural feature go from Roman imperial baths to houses and buildings in the modern world? The person we can thank the most for that is 16th-century Italian architect Andrea Palladio. Palladio was one of the preeminent figures in reviving ancient Roman forms into modern architecture, a trend we can generally refer to as neoclassicism. In the mid-16th century, he conducted the first real study of the ruins of Baths of Diocletian, and began incorporating elements of this structure into his own architecture.

His first major design to feature Diocletian windows was the Villa Foscari, completed around 1560. Piercing the mock pediment, another Classical feature, the segmented arch windows add a new geometric element to the façade. Would the Romans ever have done this? Probably not, but that's not what Palladio was interested in. He revived Roman features in new ways, incorporating them into contemporary styles and attitudes.

As Diocletian windows became more popular in elite homes, Palladio expanded the feature in to churches. The most famous of these may be San Francesco della Vigna (completed around 1570), and Santa Maria della Presentazione (1577-1580). After these facades had been completed, Diocletian windows became hallmarks of Venetian cathedrals for several years.

San Francesco della Vigna
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Diocletian Windows beyond Italy

As neoclassical architecture spread beyond Italy, so did the Diocletian window. By the 18th century, this feature made its way to Britain. In 1724, architect James Gibbs was commissioned to create a complex of structures for King's College of Cambridge. His proposal featured Diocletian windows, modeled directly after Palladio's design for the Villa Pisani. It was ultimately rejected, but the idea was there.

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