Seventeenth century military defences have been unearthed during work to protect Portsmouth's seafront.
The remains were discovered by contractors stripping topsoil from Clarence Pier playing field in Southsea as part of the £100m sea defence scheme.
Archaeologists believe they are part of the outer moat wall, which was in-filled in the late 19th Century.
Portsmouth City Council said it was "remarkably well preserved".
Last month, part of an Victorian-era seafront promenade was uncovered near Southsea Castle as part of the same project.
Alex Godden, principal consultant for Wessex Archaeology, said the latest find was likely to be part of wider defences, constructed as part of the 17th Century remodelling of earlier Tudor sea defences, according to the Local Democracy Reporting Service.
"Research and analysis of historic mapping suggests that these remains are part of the outer moat wall, which was in-filled around 1870 and then buried.
"This outer moat formed part of the fortifications, and the above-ground remains can be seen at the Long Curtain, King's Bastion and Spur Redoubt scheduled monument."
The remains have been covered up to preserve them for possible future examination.
Deputy council leader Steve Pitt said the find was "potentially nationally important".
"The discovery will allow archaeologists to confirm aspects of the defence designs which, until now, have only ever been seen on historic plans," he added.
The Southsea sea defence scheme is set to protect the coastline from Old Portsmouth to Eastney with work involving building walls, raising land and widening beaches along a 4.5km-stretch (2.8 miles) of coastline.