Archaeologists have uncovered a tower and the remains of a town wall dating back to the fourth century on the island of Tinos in the Aegean Sea, the Greek culture ministry said on Wednesday.

The discovery, near a sanctuary for the Greek god Poseidon and his wife Amphitrite, was made during construction work for an island road.

"The tower is at least two metres high and located near the modern-day town of Tinos," archaeologist Mariza Marsari told reporters.

Marsari was on the island along with the head of the Greek central archaeological council (KAS), Christos Zahopoulos, to examine the find.

So far the sanctuary, which also dates back to the fourth century, had been the island's main cultural attraction.