By Fiona Govan in Madrid. Telegraph.co.uk

A team of researchers from Spain's Higher Council for Scientific Study (CSIC) are examining a marshy area of Andalusian parkland to find evidence of a 3,000-year-old settlement.

They believe that Tartessos, a wealthy civilization in southern Iberia that predates the Phoenicians, may have had its capital in the heart of what is now the Donana national park.

Until now historians had dismissed the region as a possible site believing that it had been submerged since the ice age. But it is claimed new evidence suggests the waters may have receded in time for the Tartessians to build an urban centre, which was later destroyed in a tsunami.

The Hinojos marshes, an area close to the mouth of the Guadalquiver river where it meets the Atlantic, have now been pinpointed as the site most likely to provide evidence of a lost city.

Archaeological findings have already proved the existence of Tartessian culture at sites on the opposite bank of the river.

"If they existed on the other side, they must also have been here (in Donana)," Sebastian Celestino, the archaeologist leading the project told the newspaper El Pais.

"There were earthquakes and one of them caused a tsunami that razed everything and which coincided with the era in which Tartessian power was at its height."

Aerial photos show the existence of large circular and rectangular forms that could not have been produced by nature.

The images, together with literary accounts by ancient Greek geographers have given weight to the theory that a great Tartessian city once existed within the park.

The Tartessian civilization, which developed in southern Spain between the 11th and 7th centuries BC and became rich trading gold and silver from local mines, has long been linked by mythologists to the Atlantis legend.

While the Spanish researchers refuse to speculate on whether they are on the brink of discovering Atlantis others believe their research could be a breakthrough in a centuries old quest.

"Evidence is mounting that suggests the story of Atlantis was not mere fiction, fable or myth, but a true story as Plato always maintained," said Georgeos Diaz-Montexano, a Cuban archeologist who has spent the last 15 years searching for the submerged city.

"Atlantis is not exactly where the CSIC is looking, but it is close," he claimed.

The theory is just the latest in a long list of suggested locations for Atlantis, including various Mediterranean islands, the Azores, the Sahara desert, Central America and Antarctica.