"The tunnel, in an excellent state of preservation, was found by chance," said Eli Shukron of the Antiquities Authority, one of the two leaders of the dig.

He said the 70-metre stretch was discovered two weeks ago during excavations in the area of the City of David, the site of Jerusalem in ancient times, in what is now the Palestinian suburb of Silwan.

The tunnel is believed to have been Jerusalem’s main drainage channel at the time of the Roman conquest in 70 AD, stretching beneath the main road of the city and eventually reaching the Dead Sea, the Antiquities Authority said in a statement.

The section runs from the Pool of Shiloh in Silwan village to about 10 metres west of the Wailing Wall, the sole remnant of the Jewish Second Temple detroyed by the Romans in 70 AD.

"The channel is built of ashlar stones and is covered with heavy stone slabs that are actually the paving stones of the street. In some places the channel reaches a height of about three metres and is one metre wide, so that it is possible to walk in it comfortably," the statement said.

The excavation was led by Ronny Reich of the University of Haifa and Shukron.

"There is evidence in the writings of Josephus Flavius, the historian who described the revolt, the conquest and the destruction of Jerusalem, that numerous people took shelter in the channel and even lived in it for a period until they succeeded to flee the city through its southern end," the statement added.

The dig also turned up pottery shards, fragments of vessels and coins from the era. The Romans conquered Jerusalem in the year 70 and destroyed the Second Temple.