The city, Itil, was the capital of the Khazars, a powerful nation that adopted Judaism as its official religion more than 1,000 years ago, only to disappear, leaving little trace of its culture.
It was mentioned in medieval travellers’ accounts but Soviet dictator Josef Stalin banned any research into the city and the Khazars, fearing it would prove Russia was descended from a Jewish state.
The city made a fortune from trade but its prosperity declined and in the 14th century it was flooded by the Caspian Sea.
One of the archeologists, Dmitry Vasilyev, said: “This is a hugely important discovery. We can now shed light on one of the most intriguing mysteries of that period – how the Khazars actually lived.
“We know very little about the Khazars – about their traditions, their funerary rites, their culture.”
At their height, the Khazars, a semi-nomadic Turkic people, controlled much of what is now southern Russia, western Kazakhstan, eastern Ukraine, Azerbaijan and large parts of Russia’s North Caucasus region.
The capital is referred to as Itil in Arab chronicles but Vasilyev said the word may actually have been used to refer to the Volga River on which the city was founded or to the surrounding river delta region.
Itil was said to be a multi-ethnic place with houses of worship and judges for Christians, Jews, Muslims and pagans. Its remains have until now never been identified.
Yevgeny Satanovsky, director of the Middle Eastern Institute in Moscow, said he believes the Khazar elite chose Judaism out of political expediency – to remain independent of neighboring Muslim and Christian states. “They embraced Judaism because they wanted to remain neutral, like Switzerland these days,” he said.
The study of the Khazar empire was discouraged in the Soviet Union. Stalin detested the idea that a Jewish empire had come before Russia’s own. He ordered references to Khazar history removed from textbooks because they “disproved his theory of Russian statehood,” Mr Satanovsky added.
Archaeologists have been excavating in the area for the past nine years but have only now collected enough material evidence to back their thesis, including the remains of an ancient brick fortress.
“Within the fortress, we have found huts similar to yurts, which are characteristics of Khazar cities…. The fortress had a triangular shape and was made with bricks. It’s another argument that this was no ordinary city.”
Around 10 university archaeologists and some 50 students took part in excavations in the region this summer, which are partly financed by the Jewish University in Moscow and the Russian Jewish Congress.