Archaeologists working on a site in Oyster Street, Old Portsmouth, discovered a 15th-century jetty buried underground.
The wooden jetty, which was about 80ft wide, was the first of several quays built on the site.
Succeeding quays had been gradually built farther out to sea – resulting in the Camber Dock.
Russ Fox, who was supervising the dig, said in the 17th century a stone quay had been built on top of that same jetty.
Then houses had been built on top of it.
He also thought he had solved the mystery of why Oyster Street was given its name.
‘We have found thousands of oyster shells.
This must have been a dumpling place for them,’ he said.