Discoveries made at Southsea Castle during excavation works have given an insight into the history of the area.
A structure designed to hold a swivel mount gun dating back to the early 19th century has been exposed beneath the existing promenade in front of the castle.
It was found during excavation works for the Southsea Coastal Scheme flood defence project.
A large triangular defence structure has also been found near the gun emplacement.
It's thought to be the remains of a revetment constructed as part of the late 17th century redesign of Southsea Castle, representing an earlier phase of the historic defences.
Principal Consultant for Wessex Archaeology, Alex Godden, said: "These well-preserved remains offer a fascinating insight into the development of Southsea Castle over the past 350 years.
"The triangular defence structure appears likely to be part of the redesign of the castle by the Dutch military engineer Bernard de Gomme.
"It’s exciting that as a result of the archaeological excavations we can see the physical evidence of the large scale upgrading of the historic defences of Portsmouth that took place in the late 17th century."
“In addition, the discovery of the 19th century swivel mount shows us how the defences have been adapted and continued to evolve over centuries.”
Southsea Coastal Scheme Project Director, Guy Mason, added: "We're pleased to be working well with Historic England and Wessex Archaeology to agree on how to best adapt our design around the finds, just as we did with our design around the historic walls discovered near Long Curtain Moat.
"In the meantime our team has worked quickly to ensure the remains have been covered for protection from extreme weather and tidal conditions."