Sonar, underwater cameras and scanning equipment are being used
A medieval church which tumbled from an eroding cliff into the sea has been rediscovered by marine archaeologists.
They believe the ruins they have found are St John's church, the biggest in Dunwich which was lost to the sea off the coast of Suffolk.
Dunwich was once a thriving community before being swallowed up by the North Sea more than 500 years ago.
Experts are using the latest acoustic imaging technology to uncover clues about the lost city in the North Sea.
Stuart Bacon, director of Suffolk Underwater Studies, said: "We've found the ruins of a medieval church called St John's, which was the biggest in Dunwich.
"I've been looking for it for about 35 years so it's very exciting."
Searching for years
Mr Bacon, working alongside a team from the University of Southampton, led by Professor David Sear, said the 13th Century church tumbled down the cliffs in about 1540.
"Over the years, I've had hundreds of divers accompany me to look for it.
"We knew roughly where it was but have never been able to uncover it until now," he said.
Mr Bacon said the team had been hindered by thick layers of silt, up to two metres deep, covering the debris.
"It's like doing a survey from the air when there has been a thick covering of snow - only the tallest structures stick out," he said.
"We've got a lot more work to do to analyse the data we've collected before we can say what else is down there."
Dunwich was founded by Felix, a bishop sent by the Pope to convert the pagan Angles, Saxons and Jutes who had colonised Suffolk in the 7th Century.
It grew into a prosperous trading port and thriving city but was prone to the North Sea drift which eroded the cliffs.
By 1086, just 20 years after the Norman conquest, Dunwich was a thriving town of 3,000 people.
It had six parish churches with at least two other chapels.
It has now virtually disappeared and all that remains are a graveyard and a few old houses in the present village of Dunwich, which continues to be under threat from the sea.
Acoustic imaging identifies different densities of material on the sea bed and this helps experts to spot rocks which may be from buildings. This is how the ruins were first spotted and excavation has revealed the church.