“Incredibly rare” ancient purple dye that was once worth more than gold found in U.K.

Archaeologists working in England found a “mysterious lump” of a purple substance that would have been worth more than gold in Roman times, the researchers said in a news release.

The researchers who found the “soft purple substance” are working on a years-long investigation of Roman remains in Carlisle, England, a cathedral city in the center of the country. The dig is being led by Wardell Armstrong, a UK-based environmental, engineering and mining company

The substance was found during an excavation in 2023 of a Roman bath house. Remains of the 3rd century building exist on the grounds of what is now a cricket club, according to the press release.

The team worked with the British Geological Society to test the material. According to the statement, experts from the University of Newcastle provided further analysis and determined that it is an organic pigment containing levels of bromine and beeswax.

These ingredients allowed researchers to identify the substance as “Tyrian Purple,” the color the Roman Empire associated with its imperial court. The pigment is made from thousands of crushed seashells from the Mediterranean, North Africa and Morocco, the statement said, and was “phenomenally difficult” to make and expensive to produce, making it worth more than the gold at that time.

The discovery of the material has led researchers to believe that the building being excavated was related to the court and could even have meant that the Roman emperor of the time, Septimius Severus, had visited Carlisle. Frank Giecco, the technical director of the organization leading the excavation project, said it is an “incredibly rare” find, especially in Europe.

“It is the only example we know of in northern Europe, possibly the only example of a solid sample of the pigment in the form of an unused paint pigment anywhere in the Roman Empire,” Giecco said in the statement. “Examples of this have been found in wall paintings (such as in Pompeii) and some high-status painted coffins from the Roman province of Egypt.”