Archaeologists have begun a survey at College Green to learn more about the history of Bristol Cathedral and life in the city.
Probes will scan the entire Green over two days to build up a map of the underground graves and buildings.
Archaeologist Mark Horton said: "College Green is one of the most historic bits of Bristol, there's layers of history here."
College Green is owned by the church, but managed by Bristol City Council.
Bristol Cathedral is working with archaeologists at the University of Bristol on the project.
Dean of Bristol Cathedral, The Very Reverend David Hoyle, said: "What we're really hope to find is the sixth Saxon chapel - inside the Cathedral there is a stunning Saxon carving, a figure of Christ rescuing people from hell.
"We know there was a Saxon community here and it would be wonderful to find some evidence of that."
It is believed this chapel may also contain the relics of the patron saint of Bristol, St Jordan.
"There is an enormous debate going on about this person called Jordan," added Mr Hoyle.
"We know that St Augustine of Canterbury came here, we know he had companions with him, we think Jordan was one of them.
"We think he stayed behind and we think the chapel could be his burial place."
Depending on the weather, a follow-up survey may take place next week.