By David Keys

Archaeologists excavating near the edge of Trafalgar Square in London have found evidence of early Christianity in England, suggesting the area has a much older religious significance than was originally believed.

A team from the Museum of London has discovered a hoard of what is almost certainly royal treasure, buried in a mysterious, empty human grave laid out in the traditional Christian manner - east to west.

"Our excavations demonstrate the position as a significant and important place at an earlier date than we thought," said Alison Telfer, the senior archaeologist in charge of the dig.

The finds are among the most remarkable discoveries ever made in London and are likely to shed new light on the very early stages of the introduction of Christian ideas into the Anglo-Saxon world 1,400 years ago.

Located immediately next to one of the capital's most famous churches - St Martin-in-the-Fields - immediately to the north of Trafalgar Square, the empty grave appears to form part of a previously unknown ancient cemetery, dating back more than one and a half millennia. Archaeologists have also discovered 24 other graves on the site, all still holding the remains of their occupants.

The treasure hoard in the empty grave consists of a gold pendant inlaid with blue-green glass; glass beads and fragments of silver (possibly a neck pendant); and two pieces of amethyst, possibly earrings.

The empty grave, judging by its treasure, and several of the other early graves in the cemetery are estimated to date from the time that Bertha was Queen of Kent - 590 to 610.

"It is likely that the grave did initially accommodate a body, but the remains were removed after some months or years for burial inside a church, potentially an early version of St Martin's itself," said Professor Ian Wood of Leeds University, who specialises in 6th and 7th century history.

"It is likely that the empty grave belonged to a relative - possibly even a daughter or a niece - of the most important woman in Britain at the time, Queen Bertha, the wife of the most powerful ruler in England, King Aethelberht of Kent, overlord of the English."

Professor Wood added: "Bertha is the unsung heroine of early English Christianity because it was she, rather than the much more famous St Augustine, who was initially responsible for the introduction of Christianity into the Anglo-Saxon world. It was as a result of her activities that St Augustine was sent to England by the Pope to become the first Archbishop of Canterbury.

"The discoveries are therefore important because they reveal Christian activity, probably associated with Bertha's circle, at this very early stage of Christianity in Anglo-Saxon England."

Bertha was a devotee of the cult of St Martin. Her personal church in Canterbury, presented to her in about 590 by her then pagan husband, Aethelberht, was dedicated to the saint - probably at her behest. And her husband was, after about 597, very keen on ecclesiastical development in London, which was technically part of the kingdom of Essex but in reality under Kentish overall control.

The mysterious empty grave near Trafalgar Square may therefore have been a temporary resting place for a senior Kentish princess during the time that the Anglo-Saxon church of St Martin's was being built.

The excavations have also revealed a second mystery. At least one of the other graves was pre-Anglo-Saxon and dates from the very late Roman or immediate post-Roman period. The burial, in a stone sarcophagus, was also Christian - like virtually all the others - but was 200 years older.

This raises the possibility that the site had Christian links long before the conversion of Anglo-Saxon England, possibly as the location of a small church or mortuary chapel built there in the very late Roman period, immediately before the Anglo-Saxon pagan conquest. This would mean St Martin-in-the-Fields is London's oldest surviving ecclesiastical site, predating St Paul's by some two centuries.