By:* *Josh Davies-Jones, Stephan Turano, Eric Zhang, Kalya Chuong

At the Materials Characterization Facility in the Institute of Matter and Systems, we’re not only probing modern materials. This week, we’ve been studying the materials chemistry of the building blocks of the past.

Our latest project focuses on a fragment of history: part of the stone walls of Cetatea Poenari, the mountain citadel once home to Vlad III of Wallachia— better known to the world as Vlad the Impaler—and the enduring inspiration for the world’s most famous vampire, Dracula.

Poenari Citadel is an imposing ruin of stone and mortar perched high in the Carpathian Mountains. In the mid-1400s, it was ruled by Vlad Țepeș III, the Prince of Wallachia. He was known as Drăculea — “son of the dragon” — a title inherited from his father, Dracul, a member of the Order of the Dragon, a knightly order sworn to defend Christendom.

Vlad ruled during violent clashes with the Ottoman Empire and is still regarded as a national hero in modern Romania. But to his enemies, he was a despot and a bloodthirsty tyrant, infamous for his gruesome habit of impaling his foes.

While vampirism wasn’t a concept tied to Vlad in the 1400s, stories of his horrific deeds spread rapidly across Europe. One such story came from a Franciscan monk named Brother Jacob, who survived one of Vlad’s purges and fled westward to Germany.

There, he met a famous poet and musician, Michael Beheim, who turned Jacob’s testimony into what we’d now call a bestselling single—a ballad titled “The Story of a Bloodthirsty Madman Called Dracula of Wallachia.” Think of it as the 15th-century equivalent of a diss track, causing nearly as much fuss as a modern-day celebrity feud.

Beheim performed his chilling song across Europe, even before Emperor Frederick III of the Holy Roman Empire. And it was here, in his haunting verses, that the true myth of Dracula began:

It was his pleasure and gave him courage To see human blood flow; And it was his custom To wash his hands in it As it was brought to the table.

Following the success of Beheim’s poem, German printers began releasing illustrated broadsheets depicting Dracula’s supposed atrocities—most of them wildly exaggerated, but undeniably effective at capturing the public’s imagination. These sensational pamphlets spread the image of Vlad as a blood-drinking monster across Europe.

Centuries later, Bram Stoker would draw from these same dark tales for his 1897 novel Dracula, transforming the brutal prince of Wallachia into the immortal vampire of Gothic fiction.

The Science

Using a combination of X-ray fluorescence (XRF) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), we examined the elemental and mineral composition of a medieval brick from Vlad the Impaler’s 15th-century fortress at Poenari.

By analyzing the elemental makeup of these medieval walls, we can uncover clues about the materials, methods, and craftsmanship used to build them more than five centuries ago. Insights from these analyses can inform modern sustainable construction, guiding the design of materials and structures that could stand strong for another thousand years.

The XRF data revealed a chemical fingerprint typical of clay bricks made from local Wallachian materials:

• Si (≈48%) – Silicon, the dominant element, reflecting silicate-rich clays and quartz sands
• Al (≈16%) – Aluminum, from aluminosilicate minerals such as feldspar and clay
• Fe (≈12–15%) – Iron, from iron oxides, the source of the brick’s deep red coloration
• Ca (≈6–8%), K (≈4–7%), Mg (≈2–3%), Ti (≈1–2%), Na (≈1%), plus trace Zr, Mn, and Zn

This composition aligns perfectly with the geology of the surrounding Carpathian Mountains and known masonry techniques of the time. The Argeș River, which flows beneath Poenari, drains crystalline rocks of the Făgăraș Mountains. These rocks naturally yield zircon (ZrSiO₄) and ilmenite (FeTiO₃) grains into local river sands—both of which can be seen speckled through the brick.

These accessory minerals are highly stable, surviving firing temperatures well above 1,000 °C and cannot be formed through the brick making process. In the 15th century, hauling heavy bricks up a mountain was arduous enough; importing them from elsewhere would have been impractical. So, these minerals tell us they came from local rock and sand found around the castle.

The dominance of silicon, aluminum, and iron makes perfect sense for a medieval brick formed primarily from silicate clays. Iron oxides produced the red color, while silica provided the rigid skeletal framework.

The presence of hematite confirms that the brick was fired in an oxidizing environment, typical of medieval clamp kilns. However, the survival of some untransformed clay minerals suggests that temperatures were moderate—likely between 750–900°C—which is consistent with local masonry practices of the time.

Well-sorted quartz grains indicate that the brickmakers deliberately chose or tempered their clay with sand to minimize shrinkage and cracking. Larger and smaller grains together point to naturally mixed alluvial clay, while uniform fine grains could indicate intentional sieving. Quartz, being chemically stable, remained largely unchanged through firing, forming the hard silica backbone that contributes to the brick’s durability.

Calsium appears in the brick as part of several minerals. Most commonly, it occurs as calcite (CaCO₃), also known as lime or as gypsum (CaSO₄·2H₂O). Both minerals may have formed or re-formed during the six centuries since Vlad the Impaler’s time, as the brick weathered and interacted with its environment.

In many medieval structures, lime-based mortar was used to bond the bricks together. Over time, moisture can draw dissolved lime into the brick’s porous network, where it later crystallizes as calcite when exposed to air. Similarly, sulfur compounds from the atmosphere or from the mortar itself can react with calcium to form gypsum crystals.

The combined elemental and m data reveal a straightforward but powerful truth: the bricks of Poenari Citadel were crafted from the very earth beneath its cliffs. Local clays, river sands, and centuries of weathering come together to form the story of our bricks.

In the end, this analysis shows that Poenari’s strength comes not from myth or mystery, but from the local earth and the practical knowledge of its builders. These bricks aren’t supernatural—they’re simply well made, well fired, and well suited to their environment. And that, in its own quiet way, is just as impressive.