Rome: A team of marine archaeologists using sonar scanners have discovered four ancient shipwrecks off the tiny Italian island of Zannone, with intact cargos of wine and oil.

The remains of the trading vessels, dating from the first century BC to the 5th-7th century AD, are up to 165 metres underwater, a depth that preserved them from being disturbed by fishermen over the centuries.

"The deeper you go, the more likely you are to find complete wrecks," said Annalisa Zarattini, an official from the archaeological services section of the Italian culture ministry.

The timber structures of the vessels have been eaten away by tiny marine organisms, leaving their outlines and the cargos still lying in the position they were stowed on board.

"The ships sank, they came to rest at the bottom of the sea, the wood disappeared and you find the whole ship, with the entire cargo. Nothing has been taken away," she said.

The discoveries were made through cooperation between Italian authorities and the Aurora Trust, a US foundation that promotes exploration of the Mediterranean seabed.

The vessels, up to 18 metres long, had been carrying amphorae, or large jars, containing wine from Italy, and cargo from North Africa and Spain including olive oil, fruit and garum, a pungent fish sauce that was a favourite ingredient in Roman cooking.

Sinking puzzle

Another ship, as yet undated, appeared to have been carrying building bricks. It is unclear how the vessels sank and no human remains have been found.

The vessels are the second "fleet" of ships to be discovered in recent years near the Pontine islands, an archipelago off Italy's west coast believed to have been a key junction for ships bringing supplies to the vast warehouses of Rome.