Scientists are using cosmic ray detectors to uncover the secrets of the earliest large metropolis of the Americas.

　　Archaeologists and nuclear physicists are working together to measure the passage of muons, subatomic particles from deep space, through the 2,000-year-old Pyramid of the Sun to discover whether it was a mausoleum or a ceremonial monument.

　　They believe the experiment will lead them to burial chambers, the American Association for the Advancement of Science conference was told. Many experts believe that the pyramid, the third largest in the world, holds the mysteries of the pre-Aztec Teotihuacan civilisation.

　　Arturo Menchaca-Rocha, the director of the physics institute at the National Autonomous University of Mexico, is leading a team using muon detectors in a tunnel 26ft below the base of the 215ft-tall pyramid.

　　The ancient city of Teotihuacan, whose first inhabitants settled in the area as far back as 800BC, was the first large metropolis in the Mesoamerica.

　　It became the capital of a complex civilisation, which at its peak was made of up of an estimated 100,000 people, that lasted until it was abandoned around the seventh century for unknown reasons. Numerous excavations have failed to shed light on who founded and governed the city.