Stonehenge is a megalithic monument on the Salisbury Plain in England, about 85 miles southwest of London. It consists of a ditch and bank surrounding huge stones -- many weighing between one and 45 tons -- arranged in circle and horseshoe patterns, along with a lane connecting it to the nearby River Avon. Construction began around 3,000 B.C. and continued until about 1,100 B.C. The most common theories suggest Stonehenge is an astronomical calendar, a religious site, or a combination of the two.The story of Stonehenge wouldn't be complete without its legends. These mythical stories serve to explain the meaning of the monument, and maybe even the dangers. One such story says that the henges are gateways to where we originally came from. The legend goes on to suggest that every 5,000 years or so, someone attempts to open one of them, which bring about some horribly catastrophic event.