They also found the remains of a street – complete with furrows made by cart wheels – and a long trench that could have been used by soldiers for defence.
The remains "could – I stress, could – be the archeological traces of Naples' first port, which means we are right at the founding moment of this extraordinary city," said ancient history specialist Mario Negri of the International University of Languages and Media (IULM) in Milan, which funded the exploration.
Get a glimpse of the findings in this video:
Greek sailors are known to have founded a port in the bay nearly 3,000 years ago, naming it Parthenope after a mythical siren who supposedly washed ashore there. A larger settlement was later founded further inland as Neapolis – "new city" – and the ancient seafront became known as Palaepolis, "old city".
Today, officials suggest that the underwater ruins of earliest Naples could eventually become a tourist attraction.
"We'll have to explore a different type of tourism – underwater tourism," said Luciano Garella, who directs the city's body in charge of archeological heritage.
Exploration of the site is scheduled to continue in May 2018.