Radiates in context: chemical and archaeological analysis of the “Barbarous Radiates” coinage phenomenon in Roman Britain,
by Tasha Fullbrook, University of Reading
Tasha Fullbrook started her talk by giving us the background to how the “barbarous radiates”, crude-looking coins showing an emperor wearing a radiate crown, had arisen in the Roman Empire. She described the Augustan Monetary System (c.27 BC-c.AD 260), with one gold aureus being the equivalent of 25 silver denarii, one denarius worth 4 brass sestertii, one sestertius worth 2 brass dupondii, and one dupondius worth 4 copper asses.
However, during the Roman Empire’s 3rd century economic crisis, coins were debased and contained less valuable metals. Debased coins known as radiates were introduced by Caracalla in about AD 215 as a new silver denomination, eventually replacing the denarius. Tasha went on to describe Postumus’ revolt in AD 260, and how this led to the breakaway Gallic Empire, which included Britain. Postumus minted radiates which contained more silver than those of Gallienus, emperor of the Central Roman Empire, and radiate coins continued to be minted by other rulers of the Gallic Empire.
The Gallic Empire lasted 14 years and came to an end in AD 274, with its surrender to the emperor Aurelian. While this did much to stabilise some of the issues of the 3rd century crisis, problems with the currency continued. Aurelian’s reforms included the recall of debased radiates, and a new radiate was made with a 5% silver wash, and with the coins marked ‘KA’ or ‘XXI’ to show that they contained 20 parts of copper to one of silver.
Unfortunately, Aurelian’s reforms led to a shortage of low value small change, especially in what had been the Gallic Empire, and this is thought to have led to the production of barbarous radiates. These coins, sometimes called forgeries, are usually referred to as ‘imitations’, and appear mostly in Britain and Gaul, and in smaller numbers elsewhere in the Roman Empire.
We looked at examples of barbarous radiates alongside the official coins they were imitating, and it was evident how their name had arisen. The coins appeared quite crude, with inscriptions not always legible, but with the emperor’s radiate crown usually quite visible.
Tasha went on to tell us the aims and objectives of her project, with the main aim being to create a new framework for the study of barbarous radiates. Tasha felt that these coins had a lot of information to add to the archaeological record, especially in the wider context of late 3rd century Britain. However, their unfortunate name meant that they were often disregarded in archaeological contexts, and sometimes even thrown away.
We looked at a map of barbarous radiates in Britain, many found by metal-detectorists, and recorded on PAS. We then looked at maps of Britain showing the Roman road network, one map overlaid with sites of hoards containing barbarous radiates, and the other with both hoards and single finds. The association of the coins with roads, and especially at junctions where settlements were found, was quite clear. These were all places where official coins were found in large numbers, suggesting that the barbarous radiates were being used alongside them. Tasha explained that at sites such as Hadrian’s Wall, metal detecting was not permitted, which probably explained the relative lack of barbarous radiates found there. With little written about currency usage in the Roman Empire of the 3rd century, one can only guess how barbarous radiates were used. They were likely to have been given as change, and used to buy items of low value.
We saw how coins were made, with a blank metal disc placed between an upper and a lower iron die, and then hammered to shape the images on the obverse and reverse faces of the coin. Sometimes imitation coins were found to have the radiate-crowned head of an emperor on the obverse, but not his usual choice of image on the reverse. Perhaps a die had broken, and the coin-maker replaced it with a different obverse or reverse die. Tasha explained how die-links; coins that were linked by the dies that had been used to make them, could help determine circulation patterns.
Coin copying in the Roman Empire was strictly forbidden, with offenders punishable by death, and yet it appears from the die-links that barbarous radiates, and possibly their makers, circulated widely in Britain and Gaul. With barbarous radiates ranging in size, as well as the differing images on their obverse and reverse faces, developing a new methodology and typology for their classification is one of Tasha’s aims.
Chemical analysis of the coins to show their metallurgical composition will help greatly with their classification. Tasha explained how portable X-Ray Fluorescence (pXRF), was non-destructive and quick, enabling her to analyse up to 250 coins in one day. Microwave Plasma Atomic Emission Spectroscopy (MP-AES), takes longer and requires a 10-30mg sample, which coin curators are sometimes reluctant to permit.
Tasha showed us the preliminary results of chemical analysis of two hoards, from St Anthony-in-Meneage, Cornwall, both containing barbarous radiates as well as officially minted coins. About 150 official coins and 400 barbarous radiates were analysed. A chart displaying the different alloy types showed, for example, that while large numbers of both types of coins were found to be made of leaded copper or leaded bronze (copper and tin), a small number of barbarous radiates contained only brass (copper and zinc), leaded brass, gunmetal (copper, tin and zinc), or leaded gunmetal. Tasha is particularly interested in where the metals for the coins comes from. For example, household items, such as statuettes, may have been melted down to make coins.
Recycling of old coins was also thought to have occurred, with a large coin possibly enabling several small barbarous radiates to be made. Adding cheaper metals to increase the number of coins made was likely to have occurred. Analysis of the St Anthony-in-Meneage hoards showed increasing amounts of zinc found in the barbarous radiates, with little zinc to be found in the official coins. Coins could be made to look shiny, like silver, by being coated with tin or zinc. A graph showing surface tin versus surface silver on the coins, showed silver more likely to be present on the surface of official coins, and tin on the surface of barbarous radiates.
Tasha talked of her next steps; further case studies, at Hadrian’s Wall, Yorkshire, Norfolk, and at ‘our’ Silchester. She intends to create a working database to form the basis of her typology (and test it using some 15,000 PAS finds of barbarous radiates), a means of recreating coin colour, and intends using AI image recognition for finding potential die-links. Tasha is also looking forward to minting her very own barbarous radiates!
Report by Joan Burrow-Newton