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Janina Ramirez travels to Mexico, where, just before the outbreak of WWII, American husband-and-wife explorer team Matthew and Marion Stirling were lured into the jungle by the legend of a colossal stone head. They found the head - and a lot more than they bargained for - because it turned out to be the first clue in a trail that led to the discovery of a lost civilisation, now known as the Olmecs.

As Janina follows their footsteps through the jungle, she discovers that the go-getting Stirlings embodied the adventurous determination of pre-war archaeological explorers. Breaking new ground, the Stirlings realised that it was the Olmecs - not the much-later Mayans or the Aztecs - who built the very first pyramids, palaces and planned cities for which Central America is now so famous.

Janina's journey takes her to some of the most stunning ancient sites in Mexico, as she pieces together the evidence that led the Stirlings to the controversial conclusion that the Olmecs flourished there 3,500 thousand years ago, the same period as ancient Egypt. It is extraordinary to think, before their finds, that we not only had no idea the Olmecs even existed, but no idea any civilisation this ancient existed in Central America. The Stirlings' work was so important that, very unusually, their expeditions and excavations continued during the war, shot in glorious technicolor by National Geographic. This fantastic archive features throughout the film, intercut with Janina's modern journey.