An archaeologist says it wouldn’t surprise him if the mysterious ruins spotted by a diver dated back to the time of the Roman empire — and might even be the ancient city of Rhapta.

“It wouldn’t surprise me if it is a Roman structure, but I’d need to see it with my own eyes,” says Felix Chami, an archaeologist at the University of Dar es Salaam.

The diver who explored the ruins, Alan Sutton, says he believes the 3.7 kilometre long jumble of rubble could be that of the ancient trading city of Rhapta.

“Rhapta was in this area without a doubt,” says Chami, who has been searching for Rhapta for over a dozen years.

Evidence of Roman-era activity in the area has already been found both in the Rufiji delta and on Mafia island.

If true, Chami says it would provide evidence that Swahili civilization could be traced back to the iron age.

Read more: Ancient sunken city found off Mafia?