When it was unearthed in a Roman grave in Somerset in 1990, it was thought to signify one of Britain's earliest Christian burials - a vital clue to how Christianity spread through the late Roman Empire.
The grave, possibly that of a priest, was thought to be the earliest in Western Europe to be positively identified as Christian. Analysis of the alloy at the time of discovery failed to date the piece accurately, but showed it was closer in make up to modern sterling silver than ancient Roman silver.
The amulet find drew experts from around the world. Local councillors renamed a street and a leisure complex after it. The Archbishop of Canterbury, Dr George Carey, wears a replica of the cross.
But a leading expert on Roman art yesterday denounced the find as a fake and blamed its "discovery " on a 20th-century hoaxer. Dr Martin Henig, a lecturer in Roman Art at the Institute of Archaeology in Oxford, is convinced the 4.5cm-long amulet is a modern copy of a Roman brooch dug up in Sussex 100 years ago. The amulet's "christogram" design, an early church symbol, is similar to the design on the brooch.
"I was very excited when I heard about the amulet, but as soon as I saw it and handled it myself I was disappointed," Dr Henig said yesterday. "I experienced a sinking feeling - it was as though a reasonably good amateur silversmith had copied the Roman brooch.
"My guess is that they knew this piece of soil would be excavated and placed the piece there for a joke or because they have a grudge. It is not unprecedented."
Ian Ferris, director of Birmingham University's field archaeology unit which conducted the dig, maintains the amulet is the real thing. "Dr Henig is certainly a respected expert but we feel the context of the excavation makes the amulet's origins unimpeachable," he said.