Lighthouses are built and have existed as tools of navigations especially along coast lines to guide ships and incoming vessels as to where the sea has a shallow bottom. Certain sea beds may be shallow in certain places and deep in others and an unsuspecting craft may get marooned there. The same is true for tidal zones where high tides may sometimes cover shallow rock. Lighthouses consist of high powered bulbs and lenses to flash out a light every few seconds. In older days the light was generated using a fire but now days the few lighthouses that remain are automated. The most outstanding lighthouse was once a wonder of the world, known as the Pharos of Alexandria it stood nearly a hundred and twenty four meters high. At forty nine meters the lighthouse of Bishop Rock is the tallest in the United Kingdom.
