Stonehenge is Britain's most famous 1 monument. It consists of two circles of large standing stones, one inside the other. The inner circle consisted of arches made by laying one stone across the tops of two others. Some of these have fallen, but some are still in 2. Stonehenge was built between 3000 and 1500 BC. Nobody knows why it was built, but many people think it was to study the stars and planets or to worship the sun, because a line through its centre would point 3 to the position of the rising sun on Midsummer's Day. Since the 1980s young people have been going there for their own midsummer 4, but the police 5 prevent them from getting near the stones. Stonehenge was made a World Heritage Site in 1986.