American filmmaker credited with finding the lost Arabian city of Ubar. Clapp began researching ancient maps and literature for possible locations of the legendary city. Radar images of ancient caravan routes from NASA led Clapp and others to a site in Oman where they uncovered a large fortress. Greek and Roman artifacts found there indicated the site had been a major trading center. The team also found evidence of a sinkhole that may be the basis of the legend that Ubar was swallowed by the desert sands.