VALENCINA DE LA CONCEPCION, Spain (Reuters) - Spain's pre-historic burial chambers have survived invasion, war, a long dictatorship and a property bubble which paved over vast tracts of the country.

But the economic crisis which ended the building boom that buried some of the country's greatest archaeological treasures under shopping malls and new housing may also be bad news for those hoping to provide lasting safeguards for Spain's remaining tholos dolmens or passage tombs.

The Aljarafe region outside the city of Seville in southern Spain, with a rich Arabic and Christian history, is believed to house Europe's most extensive grouping of tholos dolmens, dating back some 5,000 years.

Many of these archaeological treasures were buried under new construction during a decade-long building craze that swept across Spain and left 1.5 million vacant homes when it ended....