Stonehenge
Stonehenge is a prehistoric monument on Salisbury Plain in Wiltshire, England, two miles west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around 13 feet high, seven feet wide, and weighing around 25 tons, topped by connecting horizontal lintel stones. Inside is a ring of smaller bluestones. Inside these are free-standing trilithons, two bulkier vertical sarsens joined by one lintel. The whole monument, now ruinous, is aligned towards the sunrise on the summer solstice. The stones are set within earthworks in the middle of the densest complex of Neolithic and Bronze Age monuments in England, including several hundred tumuli.
Stonehenge was likely and ancient solar calendar. According to a new study, a circle of 30 upright "sarsen" stones marked the days each month. Four stones on the outside of the circle tracked leap years. The top of the circle illuminated during summer solstice, and the bottom during winter solstice.