Builders discovered the ruins of an old wooden barge while working on an office development at the V&A Waterfront in Cape Town on Wednesday.
V&A Waterfront spokesperson Lynette Lambert said the discovery was made at Number One Silo in the Clock Tower precinct.
"The affected development area has been cordoned off until such time as their contracted marine archaeologist has the opportunity to assess the find," she said.
"The initial findings of the ruins appear to be that of an old wooden barge."
The discovery would be carefully examined by the marine archaeologists who had been part of the team regularly checking works since inception.
"The V&A Waterfront area is rich with history and this is not the first time that we have encountered really fascinating discoveries which form part of the legacy of Cape Town," Lambert said.
"Given the sensitivity and historic nature of the site, we have had a consulting marine archaeologist from day one. Once we have received her report, a decision will be made on the next steps."
There are several historically significant sites in the vicinity, including Chavonnes Battery, the remains of which were preserved as Cape Town's oldest major fortification after the Castle of Good Hope.
The site concerned is located between the existing Clock Tower shopping centre and the disused grain silo building.