Sri Lanka to Suffolk: Sutton Hoo and the Silk Roads

The archaeologists had their work cut out in excavating the ship, long before any precious metals glinted in the soil. That first piece of gold, found by the experienced young archaeologist Peggy Piggott, was a tiny pyramid-shaped mount, one of a pair, that had once worked like a toggle on a sword harness. Its robust gold framework was encrusted with blue and red stones. In a letter written almost immediately to the British Museum, Phillips remarked of the red inlays, 'I can hardly suppose it to be garnet'. In fact, it was.

And that was not all. A veritable gold rush occurred in the days that followed, as more and more astonishing objects came to light. The archaeologists were overwhelmed, with Basil Brown remarking in his notebook, 'When they called out to me ''We've found the treasure come and see'' I must admit that I never expected to see so much gold in any dig in this country… All the objects shone in the sunshine as on the day they were buried'. In total, more than 4,000 garnets were found in the Sutton Hoo ship burial, most of them adorning gold objects made using a metalworking technique known as garnet cloisonné. It involves the setting of garnets, as well as glass and other materials, into gold cells or 'cloisons' of different shapes and sizes, to form glittering, mosaic-like surfaces. Similar jewels had already been found in continental Europe, as well as at sites in England such as the so-called 'King's Field' cemetery in Faversham, Kent, which was excavated in the 1800s. However, the Sutton Hoo cloisonné surpassed any other known examples from early medieval Europe.

This dazzling type of metalwork is stupendously intricate – and never fails to capture the imagination. The surfaces of cloisonné objects are carpeted with tiny interlocking cells, made from narrow strips of gold, painstakingly shaped and attached edge-on to a gold sheet backing. The shapes artisans made included simple squares, plump mushrooms, serrated arcs, keen-edged arrows and many bespoke forms, specially crafted to form the bodies of predatory birds, serpents, boars and strange four-legged beasts. It is difficult to appreciate this structure when the object is well-preserved, as the garnets essentially mask it. Its intricacy only really shines through on damaged objects that have lost most of their gems.

There is even more going on beneath the surface of cloisonné objects. Each cell was filled with a paste-like blend of calcite, quartz and beeswax. This was not a glue to fix the garnet in place, the tension of the cell walls is thought to have done that. Instead, it formed a 'bed' that raised the garnets flush to the object's surface. Onto this paste, and beneath the gem itself, was the pièce de resistance: a little piece of magic that unleashes cloisonné's unique beauty. It is a gold foil, wafer thin, and usually textured with a waffle-like pattern. This tiny flake packed an enormous punch, catching the light that passed into the garnet and reflecting it back outwards, to make the stone glimmer and glow. Without it, even the finest quality garnets risked looking dull and dark. With it, the gems reached their full potential as vivid, sparkling treasures.

The Sutton Hoo objects still put on this light show today. The greatest performer is the pyramid-shaped mount unearthed by Peggy Piggott – that first piece of gold to emerge from the burial in 1939. The mount's corners are set with chunky garnets, expertly cut into three-dimensional shapes that slot perfectly into place. This method of cutting effectively made them into prisms so that, when moved in the light, the object glows from within like a miniature volcano.

The maker (or makers) of the iconic helmet from Sutton Hoo may also have exploited this effect. Researchers have noted that only one of its garnet-lined eyebrows has the special backing foils. In theory, this meant that one eye would shine while the other remained dark. Was this an allusion to the one-eyed northern European god Woden, or the simple consequence of a repair? Riddling patterns on other cloisonné metalwork hint that artisans may have coded their works with playful elements that rewarded careful attention, so a deliberate choice cannot be ruled out.

Research has revealed other remarkable things about the garnet cloisonné technique. By the time the Sutton Hoo metalworkers were crafting their pieces in the late AD 500s–early 600s, cloisonné and the use of garnets had a long history, which originated far from England. The question remains about precisely where and when the technique seen at Sutton Hoo first developed, but current thinking points towards the Black Sea, Caucasus or West Asia sometime around the early AD 200s. During the centuries that followed, the technique began to spread westwards throughout Europe, eventually becoming a badge of elite identity. By the late AD 500s, garnet cloisonné had arrived in early medieval England, reaching its zenith with the Sutton Hoo finds. The finds remained England's prime cache until 2009, when the discovery of the Staffordshire Hoard, by metal detectorist Terry Herbert, showed that deluxe garnet objects were not as rare as once thought. The hoard contained several striking pieces that may have been made in the same workshop as the Sutton Hoo jewellery, perhaps even by the same hands, due to close similarities in style and technique identified by researchers.

Materials on the move

So, the garnet cloisonné technique connects to a wide network now recognised as stretching even further afield. Perhaps the most popular question for researchers and public alike is, 'where did the garnets come from?' Historical sources offer clues. Writing in the late AD 70s, Pliny the Elder called garnets carbunculi, Latin for 'little coals' because they glowed red like fire. He linked their origin to India and Carthage (in present-day Tunisia). At around the same time as the Sutton Hoo burial, Isidore of Seville (died AD 636) identified 12 kinds of garnet. He noted that the gems were difficult to cut and that 'eastern kings' were famed for using them. However, scientific techniques have made the greatest strides towards understanding the origin of early medieval garnets.

Like other minerals, garnets form deep within the earth, appearing as crystals in rocks that have been transformed by extreme temperatures and pressures. Geological processes like erosion, weathering and the movement of tectonic plates, bring them nearer the surface and within reach of human hands, where they can be mined or, in some places, simply gathered from rocky outcrops. The cycle takes millions of years, meaning that every garnet decorating a piece of cloisonné metalwork had already lived a long life before it was cut, shaped and set by an artisan.  

Garnets occur around the world, but the geological brew in each location imbues the stones there with a unique chemical composition, like a fingerprint, characterised by different quantities of elements such as magnesium, calcium, chromium and iron. This composition holds the key to unlocking a garnet's provenance. Once identified, it can be compared to a modern library of samples collected from various places, in the hope of finding a match.

Over the years, a suite of ever-improving analytical techniques has been turned towards this task. Early on, researchers studied the chemical composition of garnets through their physical properties, including their density and refractive index (which is the degree to which a beam of light bends as it passes through a material). Another early technique called X-Ray Fluorescence (XRF), still used today, involves the firing of an X-ray beam into the garnet, causing it to emit fluorescent X-rays with properties that indicate each element inside the stone. As dramatic as this sounds, the technique is non-destructive, meaning that it does not damage the garnet or require a sample to be removed for analysis.

In 1982, British Museum scientists used XRF to examine garnets on the Sutton Hoo cloisonné metalwork. The results were mixed, partly because it was difficult to analyse garnets that were still attached to their objects. Nonetheless, the team learned that the stones were broadly similar to those decorating objects from the neighbouring early medieval kingdom of Francia (located in parts of present-day France, Germany, Belgium, the Netherlands, and Luxembourg), hinting at a common origin. Some stones differed, suggesting an alternative source that could not be determined due to the sparse garnet reference library available for comparison at the time.

Just over four decades later, in 2023, research for the British Museum's Silk Roads exhibition provided a fresh opportunity to analyse Sutton Hoo's garnets, using a far more sophisticated, and powerful, technique. 

PIXE, or Particle-Induced X-ray Emission, involves the use of a particle accelerator to fire a high-energy ion beam into each garnet. Like the XRF technique, the ion beam causes the garnet to emit X-rays, which reveal its chemical composition. Like XRF, PIXE is non-destructive but, unlike XRF, it is sensitive enough to detect even the tiniest traces of elements inside. Moreover, PIXE has no problem analysing stones that are still attached to their objects, opening a whole new realm of research possibilities. Newer tools like this, when assisted by a fuller geological reference library alongside archaeological and historical sources, have helped researchers to identify six geographical groupings of garnets used in early medieval metalwork. The deposits span an astonishing area from Scotland to Sri Lanka. This remarkable metalwork therefore embodies the extraordinary reach of networks that were active around the time the Sutton Hoo ship was buried. Where did the garnets that decorate the Sutton Hoo jewellery itself come from – close to home or further afield? 

A short walk from the famous Pyramide du Louvre in Paris, down a flight of steps and through a heavy door, is the National Centre for Research and Restoration in French Museums (Centre de recherche et de restauration des musées de France), or C2RMF for short. It is home to AGLAE, the Accélérateur Grand Louvre d'analyse élémentaire, a particle accelerator capable of performing PIXE analysis under the operation of colleagues with world-leading expertise in investigating early medieval garnet cloisonné metalwork.

In early 2023, we took five objects from the Sutton Hoo ship burial to C2RMF for five days under AGLAE's beam. It had taken months of work just to get through the door. The first task, begun in summer 2022, was choosing which pieces to take. While all of Sutton Hoo's cloisonné is exceptional, the garnets on some items stand out for their contrasting colour, size, shape, thickness or lustre, while other items differ in style and construction. These variations hint at different origins for the stones, and perhaps different workshops: intriguing avenues for scientific exploration. The final selection was a shoulder-clasp, sword pommel, imitation buckle, strap-distributor, scabbard button and a pyramidal mount – perhaps the very one unearthed by Peggy Piggott, or its twin, found soon afterwards.

The next task was to apply to visit C2RMF through a scheme run by IPERION HS, a research consortium that funds access to world-leading scientific instruments, like AGLAE, in laboratories across Europe. Excitingly, the application succeeded, triggering a complicated logistical operation to transport the objects to Paris, involving dozens of colleagues and another funding application to cover the costs therein. The hard work paid off. In late February 2023, deep beneath the pavements of Paris, the Sutton Hoo garnets began to give up their secrets.

The particle accelerator AGLAE is an imposing sight. It fills an entire room at C2RMF and the Sutton Hoo metalwork looked tiny in front of its finger-like beam and detectors. Each object was carefully positioned on a platform within reach of AGLAE's ion beam. If the object was an awkward shape, a piece of polyethylene foam was cut on the spot to make a cradle or prop to hold it safely in just the right place. Finally, the beam's firing button was pressed, giving a moment to make a safe but hasty retreat outside to computers that would display the first data from the garnets.

AGLAE was operated by engineer Quentin Lemasson and senior researcher Dr Thomas Calligaro, who worked tirelessly like a tag-team so that analysis could continue around the clock. Watching a live feed from AGLAE's room, they used a computer to move the beam remotely from garnet to garnet, looking for a tell-tale white dot that showed it was in the right place. This was painstaking and time-consuming work – some objects contained hundreds of garnets and some garnets were just millimetres across. The shoulder-clasp alone took more than a day to analyse. My role was to record which garnets were 'done' by numbering them in sequence on a photograph. These diagrams alone bring home the precision and focus involved.

While the set-up took time, data came through almost as soon as AGLAE's beam hit the garnet. Instantly, a graph popped up on-screen revealing the chemical elements in the stone. C2RMF's team, who have analysed thousands of garnets over many years, could estimate the garnet's probable origin just from the graph's shape. These early results soon began to sketch out the story of the Sutton Hoo garnets. They indicated that all five objects were decorated with gems from India, Sri Lanka and Czechia. While incredible to learn, this was expected, as AGLAE had identified similar stones upon objects in the Staffordshire Hoard, which have potential links to the Sutton Hoo workshops and, because garnets on several of the objects had different hues, hinting that they had different origins. The scabbard button is the most dramatic example. Its dome is decorated with a cross of orange-hued Sri Lankan and Czech garnets against a background of purple Indian stones so that, when lit, the cross appears to glow against darkness.

There were surprises, too. While four objects combined garnets from at least two geographical sources, the stones analysed on the imitation buckle appeared to come exclusively from India. The region supplied large, high-quality stones that are clearly present on the buckle; but even its tiny paler-hued gems, which on the other objects tended to be of Sri Lankan or Czech origin, seem to have come from the Indian source.

The final, fully analysed results are still to come, but until then it is possible to speculate over what they might reveal about the long-distance exchange of materials and ideas, as well as knowledge of the wider world, in early medieval England. Did the makers of the Sutton Hoo pieces choose garnets for their colouring, or did their origin also influence their decisions? This is an especially tantalising question for the imitation buckle. If the final results confirm the Indian origin of its gems, could this knowledge have added to their appeal, infusing the buckle with special meanings linked to the faraway land where they formed? We can only speculate.

The Sutton Hoo ship burial is often described as a microcosm of the early medieval world, because it contains objects from so many different places, ranging from western Britain and Ireland to the eastern Mediterranean and Asia. Research is refining this picture even further. Every piece of garnet cloisonné metalwork from Sutton Hoo is its own microcosm, representing a transcontinental fusion of ideas and materials that took place centuries before the globalised networks we know today. The technique of setting lustrous gems into elaborate cell patterns reached England after travelling thousands of miles from its origin far to the east. The stones filling each cell made their own epic journey from as far as southern Asia, where they formed underground millions of years before. It is fitting that these stories are being revealed today by another kind of international collaboration, as ideas and technologies are exchanged across the world – just as they were 1,400 years ago, when the Sutton Hoo ship made its final voyage into the Suffolk soil. 

With thanks to Dr Thomas Calligaro and Quentin Lemasson at C2RMF. Access to AGLAE was provided through IPERION HS, a project funded by the European Union, H2020-INFRAIA-2019-1, under GA 871034. Additional thanks to British Museum colleagues Andrew Meek, David Packer, Lucy Romeril, Chris Stewart, Richard Wakeman and others who organised transportation of the objects to Paris.

The finds from Sutton Hoo were donated to the British Museum by Mrs Edith Pretty.