The Pharos Lighthouse. The seventh wonder of the world stood for 17 centuries, guiding sailors to the coast of Egypt. No one really knows exactly what it would have looked like or even how it worked. Concluding a four-part series, Aubrey Manning meets the archaeologists who have found its remains underwater and are piecing togetherthe clues to unravel its secrets. ProducerPam Rutherford. E-MAIL: scirad@bbc.co.uk