Sometimes it takes a village to raise a window. Between 2015 and 2017, skilled masons meticulously carved and beveled arches and four-lobed flourishes for a Gothic-style stone window frame in Guédelon Castle’s ornate Chapel Tower. All that remained was to install some glass. But there was a problem, and the carpenters, painters, blacksmiths, basket weavers, historians, and archaeologists who work on-site were all enlisted to figure it out. Eight years later, the matter of what to put in the window of a medieval castle has nearly been resolved…maybe.
Luckily, the team of 40 professional builders and craftspeople at Guédelon Castle love a conundrum. The castle, located in an abandoned quarry in the Puisaye region of Burgundy, 100 miles southeast of Paris, is the site of one of the world’s most comprehensive and longest-running experimental archaeology projects. In this kind of undertaking, archaeologists partner with skilled laborers to test hypotheses about how people worked, lived, and built in the past, filling gaps in academic knowledge through real-world trials. The project launched in 1998 with a straightforward mandate: Build a thirteenth-century castle using only thirteenth-century tools, techniques, and materials. Medieval archaeologists would provide guidance. And the hope was that every obstacle would reveal something that historians, architectural researchers, archaeologists, and castellologues, or scholars who specialize in studying castles, didn’t know. “At Guédelon, we’re looking for what disappeared in traditional archaeology,” says Florian Renucci, the master mason and longtime site director at Guédelon, who was formerly a researcher at Sorbonne University. “Experimental archaeology means bringing to life what workers can do. We’re always looking, hearing, feeling. Now, with our work, the castle can speak.”
Guédelon Castle, in the Puisaye region of north-central France, represents a modern effort to build a thirteenth-century castle using only construction materials and techniques employed by medieval builders and artisans. After several decades, masonry work on the castle’s Chapel Tower (top left) and the adjoining Great Hall is now complete.
The first thing the castle said about windows is that they couldn’t have been made of glass. Guédelon’s artisans and committee of scientific advisers are constantly scouring medieval texts for clues about how thirteenth-century builders would have handled such details. In the castle’s imagined backstory, the fictitious seigneur, or lord, of Guédelon was a cash-conscious minor noble trying to make a home in 1228, putting him—and today’s builders of Guédelon—at the mercy of his financial circumstances. In that era, glass was extraordinarily expensive and reserved for places of worship and royal residences. Glasswork, the team learned, swallowed up half the cost of building a cathedral. Unfortunately, whatever material was used to fill the window frames of lesser edifices has left no traces in the archaeological record.
Artisans, many wearing period garb, initially tried to fashion goatskin panels for the Chapel Tower window after learning that this material had been used in contemporaneous buildings—but the panels warped in the winter frost and cracked in the summer heat. The team then reviewed a list of prices for the materials used to build the Palais des Papes, or Palace of Popes, in Avignon, which was begun in 1252. They learned that humble linen, stiffened with beeswax, once covered some windows at this grandest of châteaus. Valérie Lachény, Guédelon’s master painter, decorated linen canvases with an eye-catching design of golden oak leaves ensconced in maroon semicircles—a pattern inspired by twelfth-century stained glass at Strasbourg Cathedral in northeastern France. In spring 2025, three painted linen panels could be found propped in her workshop, each waiting to be affixed between wooden frames engineered by the castle’s carpentry atelier to fit into the tower’s stone window molds. Each frame takes 150 hours to join, rasp, carve, and assemble.
Decorated linen window panels (left) stand in the Guédelon painters’ atelier, awaiting installation in the Chapel Tower. Patterns from twelfth-century stained glass at Strasbourg Cathedral (middle) inspired the panels’ designs. One linen panel (right) in the Great Hall’s antechamber has already been put in place.
Meanwhile, an ongoing debate about how to fasten the linen to the frames rages. Guédelon’s blacksmiths have forged bespoke iron tacks, but, as carpenter Simon Malier explains, this option for attaching the fabric requires finesse, lest the wood crack. The basket weavers have suggested sewing the linen into the frames with a cow-horn needle. “For this kind of thing,” Malier says, “it’s a team effort.” Whatever method wins out, when the window is finally mounted, the waxed linen exterior will be brushed with flaxseed oil to protect it—which may or may not work. Recently, Malier says that he, Renucci, and Lachény stumbled on a snippet of medieval text describing a tantalizing linen window coating that shines “like crystal.” “But we don’t have the bloody recipe!” he laments.
“Because the Guédelon team works in the conditions of thirteenth-century laborers, they discover techniques that people were figuring out at that time,” says archaeologist and Guédelon project scientific committee member Nicolas Faucherre of Aix-Marseille University. “That’s why Guédelon is so important for archaeologists.” Every detail must be considered, and there are no shortcuts. The site is an unparalleled experimental archaeology project and may remain never-quite-finished forever. By observing the work of the castle’s “medieval” builders, archaeologists and other scholars have discarded old ideas and hatched new ones about how monuments of the era were created. They have solved mysteries about how ceramic for tiles was mixed and fired, how lime mortar was troweled to hold structures fast and make them last, and how scaffolding was erected to reach dizzying heights. Some discoveries may seem esoteric, but each one can help refine scholars’ understanding of tens—or even thousands—of medieval sites.
In 1995, Faucherre and archaeologist Christian Corvisier found something quite striking while studying Saint-Fargeau Castle, 5.5 miles northwest of Guédelon. The château there was built from the fifteenth through the seventeenth century, but the archaeologists discerned the foundations of a smaller, earlier fortification with thirteenth-century characteristics beneath it. The château’s owner, Michel Guyot, became intrigued by the prospect of rebuilding the earlier structure. So, he bought the disused quarry in Guédelon Forest in the commune of Treigny and embarked on the adventure with cofounder Maryline Martin, a young businessperson. Instead of imitating Saint-Fargeau Castle, they decided, the new structure would be an original, loosely following the model of Ratilly Castle, which had been built around 1270 just two miles south.
“When I came here for the first time, it was just forest,” says Martin, who is now the owner of Guédelon. “But we had a lot of luck.” The forest, 370 acres of which belong to Guédelon, has ample oak for timber, a lode of iron-streaked sandstone that serves most of the masons’ and blacksmiths’ needs, and seemingly bottomless pockets of colorful minerals for the painters to extract pigments from. “It’s incredible for me to imagine how many solutions we have just within sight,” Martin says.
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