Groundbreaking research sheds new light on 'majestic' Roman monument
University of Glasgow expert pinpoints previously unknown recipe used to create gold decoration
It is a breakthrough which sheds new light on one of the most mysterious cults in Roman times, and reveals previously unknown techniques employed by artists creating a monument in honour of an ancient deity.
Experts at the University of Glasgow have revealed “paradigm shifting” new findings about an altar used by Roman soldiers to worship the god Mithras, during their postings to a fort on Hadrian’s Wall.
A cutting edge analysis of the near two thousand year-old artefact has uncovered the first known use of a palette of pigments that gave the altar a glowing golden surface, resulting in a “majestic” monument for worshippers of the divine guardian of covenants, oaths, truth, and light.
The altar was excavated from a Mithraeum in the southwest corner of the Carrawburgh Roman fort, located just south of Hadrian’s Wall, in 1950. But the exact detail of how it was created and decorated has remained a mystery until now.
Thanks to groundbreaking techniques, Dr Louisa Campbell, a lecturer in heritage materials science at the university, discovered that the panel was covered in a golden surface crafted from a previously unknown recipe featuring pyrite, also known as fool’s gold.
The pyrite was mixed with beeswax, which created a shiny, spreadable material, and gave the appearance of gold gilding. According to Dr Campbell, the imposing finish helped to elevate the monument to an “entirely unprecedented level,” and ensured that the altar would have exerted a powerful pull on those Roman soldiers and other Mithraic adherents who entered the darkened temple for worship.
“These deliberately darkened spaces offered an opportunity for Roman soldiers to enact certain roles in secret, cementing their hierarchical position within both the army and the cult,” she told Scotland on Sunday. “Bouncing open flames from lamps off an elaborately decorated golden inscription panel would have enhanced the performance of each initiate, casting shadows in some areas and reflecting light on others created a deeply enigmatic ambiance unique to Mithraism.
“Religious practice was pivotal to the Roman military personnel in these frontier zones, as evidenced by the many altars left behind, and this particular altar offers a unique insight into how carved stones were dressed up to resemble high status gold inscriptions to elevate cult activities.”
Carrawburgh, known to the Romans as Brocolitia, was one of 16 large forts along Hadrian’s Wall. The fort housed about 500 soldiers, first from south-west France and later from other north-western provinces of the Roman Empire. It was built later than the other forts on the Wall, perhaps around AD 130, and may have kept its garrison until shortly before Roman rule in Britain came to an end.
The small and secluded rectangular stone temple to Mithras had one entrance, and is unlikely to have had any windows, so as to recreate the atmosphere of a cave. According to English Heritage, who manage the site on behalf of Historic England, the temple was rebuilt or refurbished four times. It had fallen out of use by about AD 350, by which time it had suffered some deliberate desecration, with robbers looting its stones for building materials.
In its heyday, however, the temple and the main altar - dedicated by Marcus Simplicius Simplex, the commander of a military unit, probably the first Batavians - would have been a central part of the settlement, located near Hexham in modern-day Northumberland.
Dr Campbell, who used digital reconstruction to produce an image of what the altar would have looked like for Roman audiences, described it as a “powerful and hugely impactful monument.”
The process of establishing how the buff sandstone altar would have appeared to Roman worshippers of Mithras involved non-invasive microphotography and a technique known as portable X-ray fluorescence, allowing Dr Campbell to examine the surface of the stone and establish the composition of the surviving pigments.
She then used infrared spectroscopy and X-ray diffraction on samples to scrutinise them in greater detail - an approach she described as a combination of “archaeological investigation and scientific analysis.”
Such work was complicated by the fact that interventions by previous generations of conservators trying to reconstruct fragmented sections at the top of the altar had damaged some surviving pigments. However, enough remained to allow Dr Campbell to discover something entirely new.
Together with Dr Margaret Smith, an affiliate research fellow in archaeology, and Dr Sarah Dugmore, an analytical services technician at the university’s school of chemistry, Dr Campbell’s findings have been published in Colorants, an international-peer reviewed journal
The subsequent digital images, she said, were “striking and entirely unexpected,” with the identification and testing of what looked like traces of gold overlays on several areas of the panel leading to a significant breakthrough.
“Pyrite has never previously been recorded as a pigment,” she explained. “This result breaks new interpretive ground and transforms our understanding of the materials Roman artists were exploiting for their palette.”
She said the panel in question had been decorated using a “highly complex” practice of pigment mixtures in order to depict sculpted and inscribed features, with the analysis even allowing her to understand the order in which the work was carried out.
“The consistency of elevated elemental peaks across the panel, including letters, confirms the entire panel was painted purple in advance of letters being depicted in cinnabar/vermilion red,” her paper explains. “Then the background was painted gold, not necessarily contemporaneously.”
The confirmation of the purple paint base, Dr Campbell added, was also a “groundbreaking” and “deeply enigmatic” finding that transformed our understanding of how Roman artists inscribed sculptures.
Dr Campbell is now working with the National Museum of Scotland to assist with a major new exhibition featuring altars excavated from a Roman fort at Inveresk. It is hoped she will be able to apply the techniques used in her analysis of the Carrawburgh altar to reveal previously hidden layers on the Inveresk artefacts, which also once had pride of place in a temple to Mithras.
The exhibition, ‘Roman Scotland: Life on the Edge of Empire’, will run from 14 November 2026 to 28 April 2027.
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