Scientists believe that the enormous stones were transported from places around the country - some up to 240 miles away - to their present site on Salisbury Plain in southern England. Work on the monument is thought to have started around 2000 B.C and continued to 1500 B.C. Today,engineers estimate that approximately 600 people were needed to transport each sarsen stone from its point of origin to Sailsbury.Scientists consider this a remarkable feat, given that heavy lifting equipment used in modern construction was not available at that time.