In 1993 a fragment of a Roman finger-ring made of jet was excavated from the gravel and silts of the Windle Brook in the garden of 42 London Road, Bagshot.  Phil Stevens wrote of this excavation:

During the very late Roman period, when the areas of hard and compacted gravels formed the exposed land surface 2 grave pits were dug with approximate east-west alignments. The high acidity of the ground water has resulted in the total destruction of all bone material. The presence of a body could only be identified by brown silty stains. 

Roman period jet ring from Bagshot. Courtesy of Surrey Heath Archaeological and Heritage Trust.  Ref: A/93/38 151 60

The grave goods were few and unremarkable except, quite unexpectedly, for a significant part of an engraved finger ring fashioned from jet. This ring, associated with the late pottery shards and with the grave's general stratigraphy, dates the burial to late 4th or early 5th century. It is stylistically Roman with its raised bezel. On this has been engraved the CHI-RHO monogram. In its own right it is unique and forms part of the relatively rare evidence of Christianity in this country in Roman times ¹.

The original identification of the ring as a grave artefact is now regarded as doubtful.  

History of the Chi-Rho Symbol 

Constantine was the first Christian Roman emperor. Around 307 AD, before a great battle where he and his army were outnumbered, legend has it that he had a vision of  a Chi Rho symbol - the first two letters in Greek for "Christ" - (XPICTOC).  Emerging from the battle victorious he promptly converted to Christianity and adopted Chi-Rho as his symbol.  Constantine made great use of the Chi Rho on coins, shields and standards of his Roman legions.

The symbol on the Bagshot jet ring is a later style which replaces the letter chi with a cross and is hence called the Rho-Cross symbol.  Hence the ring is believed to have been engraved not earlier than 390AD and most probably in the early fifth century.

The best source of jet in Britain, indeed in Europe, was and is, at Whitby on the Yorkshire coast.  In Roman times a considerable industry flourished there.  It is therefore likely that the ring was manufactured at Whitby; but it may have been engraved to order when traded locally; maybe in the market at the local capital at Silchester.

Unfortunately, we cannot definitely say that Christians inhabited Bagshot since the locational value of rings is low since they could have been stolen or lost while the owner was travelling.   Although the ring shows signs of wear, it does not show abrasions which would have occurred had it been washed down in a stream; and hence it was probably lost where found.

Jet appears to have been predominantly used for female jewellery; especially jet rings, being relatively fragile.

But this ring is size 'S' which is normally a man's size.

The Bagshot ring is unique in that although the chi-rho and the more unusual rho-cross symbols were used on other rings found in Britain; none were made of jet.  Illustrated below is the more usual type of ring.

	The Brentwood Ring Replica of a late 4th century gold ring found in Brentwood, Essex. It is a seal ring with a chi-rho symbol in reverse and is the earliest Christian ring found in Britain. There is also a similar ring in the Vatican museum.
	The Richborough Ring This is a copy of a late 4th century ring found in Richborough Castle, Kent. It has a chi-rho symbol on the bezel and the inscription reads IUSTINE.VIVAS.IN.DEO - "Jusinius, may you live in God".

References:-

1    Surrey Heath in the Dark Ages,  Phil Stevens, 1994. p4

A detailed analysis of the ring appears in the Oxford Journal of Archaeology, Vol 21, No 2, p211 "A Rho-Cross Engraved on a Jet Finger-Ring from Bagshot, Surrey".  Tamasin Graham, 2002.