Through carbon dating research, an incredible find has been uncovered in Transylvania, Romania. Nothing less than a medieval fortress has conclusively been proven to be built by the Knightly Order of Teutonic Knights.
The Teutonic Knights evoke a myriad of medieval legends. From chivalrous sacrifices to save women and children from harm to formidable raids to prevent attacks by pagan groups, medieval peasants celebrated the Knights’ monastic devotion and military skill. Their mission was sacred: to allow civilization and Christianity to flourish. Their work began initially by providing medical care for the sick and wounded pilgrims setting out on pilgrimage into the Holy Land in 1190, with a field hospital in Acre during the Third Crusade. In 1198, they were sanctioned by Pope Innocent as an independent military and chivalric order.
The Knights served during a time of superstition. Medieval peasants were convinced that dark spirits lurked in the dense forests that extended for miles. Society was tormented by famines, sickened by plagues, and beset by violence. But they just weren’t skilled in warfare or medicine; these knights were also castle builders. The Teutonic Order would construct fortresses to provide shelter to the community. With the support of the Holy Roman Emperor, they acquired land and souls for the Empire.
The now fully restored Feldioara Fortress or Marienburg Castle, in Brasov County, Transylvania, Romania. (Rotaru Florin/CC BY-SA 4.0)
Teutonic Knights Expand the Holy Roman Empire
The Crusader castles and fortresses became landmarks of the Empire. They were arrayed along coastal regions and even into the interior of the Levant, such as the famous Montfort Castle in northern Israel that served as a treasury and central archives of the order. Rather than concentrating the forts in specific provinces, the Knights built in strategic locations that could delay the enemy until reinforcements arrived. Having a network of forts discouraged sieges because opposing forces would find it difficult to attack multiple locations with intensity. The castles and forts protected trade routes and boosted the economy of Christian monarchs. These forts were beneficial because they supported the community and fostered political agreements between the monarchs. The Knights’ intervention relieved small kingdoms from having to take on expensive building projects.
In 1211, the Teutonic Order expanded to Eastern Europe at the invitation of King Andrew II of Hungary. He settled the Knights in Transylvania to guard the southeastern border of his kingdom against attacks by the Cumans, a loosely knit nomadic people who had raided back and forth across the Danube River for hundreds of years. Though the Knights were successful in controlling border hostilities, they overstepped their authority. Historical records from this time period show the Knights expanded their presence beyond border defense. They began constructing a Teutonic stronghold, Feldioara Fortress, a fortification of earth and wooden palisades, using property in Burzenland gifted to them by King Andrew. The name meant earth castle, but the Knights renamed it Marienburg, Mary’s Castle, after the patron saint of the Teutonic Knights. They built a masonry foundation and a wooden fortress. The Hungarian crown eventually expelled them in 1225 after fears grew over their rising independence.
The Unintended Consequences of Knights’ Assistance
In 1226, a powerful Polish duke, Konrad I of Masovia and Kuyavia, asked the Knights to help protect his lands on the lower reaches of the Vistula River. He intended to defeat the pagan Prussian tribes along his borders and expand his lands into Chelmno in Prussia. His previous attempts to defeat Prussian forces had failed, resulting in a long border war. The Prussians terrorized the Polish peasants and threatened the Duke’s castle. The Holy Roman Emperor, Frederick II, issued the Golden Bull of Rimini, granting the Knights imperial authorization to conquer the region. Led by Herman of Salza, the Knights took possession of Chelmno and spread Christianity. The Holy Roman Empire would rule Prussia, and the Knights would own the land they had defended.
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Largest Extent of the Teutonic Order as a State (Wikimedia Commons/CC0 1.0)
Archaeological Excavations and Radiocarbon Dating
For decades, researchers have viewed Feldioara as one of the strongest candidates for a Teutonic center in eastern Europe. Originally, the fortress had two fortified sections. One fortified section protected the nearby settlement and parish church. The second fortified section stood on an isolated hill separated by a natural gorge. Medieval defenses on the hill included several towers placed toward the cardinal directions and a fortified entrance gate.
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Fortress Feldioara (Saturnian/CC BY 3.0)
Using Scientific Analysis To Date the Fortress Construction Materials
When the researchers were finally able to examine the mortar, they found that the material absorbs carbon dioxide from the atmosphere. Depending on environmental conditions, the process can last for years or even centuries. To provide an accurate analysis, the research team isolated microscopic calcite particles from thirteen mortar samples collected at the fortress.
Scientists assessed the purity of those particles with FT-Raman spectrometry before conducting accelerator mass spectrometry radiocarbon dating. The team also compared the results from their lab with archaeological evidence, stratigraphy, and written historical records. Researchers also used the OxCal statistical program to match the measured radiocarbon values set within the narrowed historical window of Teutonic occupation between 1211 and 1225.
The study raised new questions about this particular site’s history. One mortar sample from beneath the church apse pointed toward construction activity even before the arrival of the first Teutonic Knights, who took possession of the land. This construction activity was possibly linked to earlier Western colonists in Transylvania. Another sample suggested certain parts of the church dated to the 13th century and could even have been connected to the Cistercian Order, which received Feldioara in 1240 after the knights' expulsion.
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Settling the Debate with Technology and Historical Research
By combining radiocarbon analysis, chemical screening, and statistical modeling with traditional historical research, the team constructed a timeline stretching from the 12th century AD to the early 19th century AD. Their findings settled a debate that had lasted nearly eight centuries. The analysis of Feldioara provides conclusive scientific proof of a Teutonic stronghold in Transylvania and offers a clearer picture of how crusader military architecture spread through eastern Europe during the Middle Ages.
Top image: Romania, Feldioara Medieval Fortress, before restoration. Source: A. Ioniță/Nature
By Ramsey Hardin
References
Carvajal, Guillermo. “Researchers Discover the Teutonic Knights Built Feldioara Fortress in the 13th Century to Create Their Own Independent State.” La Brújula Verde, May 29, 2026.https://www.labrujulaverde.com/en/2026/05/researchers-discover-the-teutonic-knights-built-feldioara-fortress-in-the-13th-century-to-create-their-own-independent-state/?
Radley, Dario. “Radiocarbon Dating Confirms Teutonic Knights Built Feldioara Fortress in 13th-Century Transylvania.” Archaeology News Online Magazine, May 30, 2026.https://archaeologymag.com/2026/05/teutonic-knights-built-feldioara-fortress-in-transylvania/
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