Archaeologists have discovered man-made stone structures cleaned up by December's tsunami.
Some think the port remnants are part of the mythical city of Mahabalipuram, which legend says was so beautiful that the gods sent a flood that engulfed six of its seven temples.
Other relics were also revealed when the powerful waves washed away sand as they smashed into the Tamil Nadu coast.
The Archaeological Survey of India launched the diving expedition after residents reported seeing a temple and other structures as the sea pulled back just before the tsunami hit.
The new finds were made close to the 7th Century beachfront Mahabalipuram temple, which some say is the structure that survived the wrath of the gods.
Other discoveries made at Mahabalipuram earlier this month include a granite lion of a similar age to the temple that experts believe had been buried for centuries before the tsunami shifted the sand.
Archaeologists have been working at the site for the last three years, since another diving expedition discovered what appeared to be a submerged city, including at least one temple.
The myths of Mahabalipuram were first written down by British traveller J Goldingham who was told of the 'Seven Pagodas' when he visited in 1798.
Andrew Zilouf
Tsunami Washes in Ancient Remains
Divers have unearthed more evidence of an ancient port city off the South Coast of India.
