Volunteer divers have photographed and plotted 25 man-made features at the site of Shipden, a British town swallowed by the sea off the coast of Norfolk around 700 years ago.
The flint-built remains were found several hundred metres from the beaches of Cromer, a coastal town on the eastern coast of England.
They are believed to form part of the original medieval settlement, which was gradually consumed by the advancing North Sea during the 14th century.
Following early morning starts at Sea Palling, a village further down the Norfolk coast, the volunteer divers travelled to explore the seabed off Cromer.
The team from the Anglian branch of the British Sub-Aqua Club, the national governing body for scuba diving in the United Kingdom, took advantage of clear skies and unusually still water during the summer.
The conditions exposed the chalk and sand of the seabed, allowing the divers to record features which may otherwise have remained hidden.
Working alongside local historian James Mindham, the team located and photographed around 25 man-made features.
They include a line of flint structures, the lower sections of stone caissons, and other pieces of cut stone.
Caissons are watertight retaining structures used to allow construction work to be carried out underwater.
Some of the structures remain standing between eight and ten courses high, despite having spent centuries underwater.
First underwater photographs
Specialist photography has allowed preliminary 3D models of the finds to be created.
The images are believed to be the first ever taken of the underwater features.
Researchers are investigating whether the caissons formed part of a 14th-century attempt to hold back the North Sea.
They could alternatively be connected to a pier authorised in 1390.
The Alfred Savin project, an initiative that explores the history of the local area, stressed that these remain theories rather than firm conclusions.
The lost settlement of Shipden
Shipden was once a thriving settlement on the north Norfolk coast.
The Domesday Book, a comprehensive survey of England and Wales completed in 1086 by order of King William the Conqueror, recorded the town as having 117 residents.
The survey noted three acres of meadow, a harbour and two churches.
The woodland was recorded as being capable of supporting 36 pigs.
Its name gradually fell out of use during the 13th and 14th centuries and was replaced in historical records by Cromer.
Centuries of coastal erosion consumed the original settlement.
The devastating North Sea storm of January 1362, which caused widespread damage across England and northern Europe, was among those to batter the coastline.
Church Rock folklore
The disappearance of Shipden later inspired generations of local folklore.
The most famous tale claimed that the tower of St Peter's Church survived beneath the waves on a geological formation known as Church Rock.
Some historical accounts said the ruins could be glimpsed at particularly low tides.
Local legend also claimed the church bell could still be heard tolling during storms, or warning fishermen not to go out to sea.
Historical documents confirm a church was lost to the sea, but the latest divers found nothing that could be positively identified as the building.
Researchers now believe Church Rock may not have been the church at all.
St Peter's is thought to have stood further north and west of the site explored by the divers.
Challenging local legends
Peter Stibbons is the chairman of the Friends of Cromer Museum and director of the project.
"Those of us brought up in Cromer have always known the story of Church Rock, so it's a big step to saying the legend may be incorrect," Stibbons said.
"We're busy going through the medieval documentation and matching it to the physical finds to date, to suggest a better understanding of Shipden. For the present we're putting forward ideas rather than conclusions."
The mystery became more tangled in August 1888 when a Great Yarmouth pleasure vessel called Victoria struck a rock just beneath the surface of the water.
Those on board the boat were rescued, but attempts to free the vessel failed.
The wreck and part of the obstruction were later blown up because they posed a danger to commercial shipping.
The explosion may have destroyed archaeological evidence, with divers finding scattered flint which could have come from the demolished structure.
Next steps for the expedition
Lead diver Nick Schiller said the initial interest was in the possibility of there being more remains from the Victoria.
"However, it's been a bonus to help the Cromer team to take some steps forward in understanding the town of Shipden and the port of Cromer," Schiller said.
"It looks as if the supposed 'church rock' turns out to be a flint-built structure from medieval sea defences, so the hunt for a church site can go on together with investigation of other significant features."
The diving team said the summer work had greatly enlarged the scope of the investigation but raised more questions than it solved.
The diving season has ended, although the team hopes to explore the site again next year.
Findings and 3D reconstructions will be published online and displayed at Cromer Museum.
The research forms part of the Alfred Savin project, supported by The National Lottery Heritage Fund, a fund that distributes money raised by the National Lottery to heritage projects across the United Kingdom.
