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An ancient sunken city has been found off the Egyptian coast and its treasures uncovered by French underwater archaeologist Franck Goddio.

Thonis-Heracleion, the Egyptian and Greek names for the city combined, was only known in ancient classic texts and had been almost forgotten by mankind.

But in 2000, Goddio and his team from the European Institute of Underwater Archeology (IEASM) were able to locate the city, map it and excavate it using sophisticated technical equipment.

Before 331 BC, Thonis-Heracleion was a prosperous port of entry to Egypt and was used by all ships coming from the Greek world.

It was also home to the temple of Amun, which was a key element to the rites associated with the continuation of the dynasty.

Greek historian Herodotus told of a great temple built where the hero Herakles first arrived in Egypt, and wrote of Helen of Troy's visit to Heracleion with her lover Paris before the Trojan war.

Thonis-Heracleion extended around the temple and a network of canals, which the researchers think gave it a lake-like appearance.

The ancient city was founded around the eighth century BC. However, it witnessed a host of natural catastrophes and finally sunk into the abyss around the eight century AD. Now located around 6.5km from the coast of Alexandria, for 1,200 years it lay undisturbed.

During his excavations, Goddio found objects showing the city's glory, including huge statues, inscriptions, jewellery, coins, ritual objects and ceramics - all preserved under the sea and frozen in time.

A statement from Goddio's website said: "The quantity and quality of the archaeological material excavated from the site of Thonis-Heracleion show that this city had known a time of opulence and a peak in its occupation from the sixth to the fourth century BC. This is readily seen in the large quantity of coins and ceramics dated to this period.

"The port of Thonis-Heracleion had numerous large basins and functioned as a hub of international trade. The intense activity in the port fostered the city's prosperity."

Goddio said that while they have discovered the city, it will take many years for them to uncover its secrets.

He told the Daily Telegraph: "We are just at the beginning of our research. We will probably have to continue working for the next 200 years for Thonis-Heracleion to be fully revealed and understood."