Stonehenge

An outer ring of sarsen stones about four metres high and twenty-five tons apiece, topped by lintels held with mortise and tenon joints, a piece of carpentry in stone found on no other monument of its time. Inside is a ring of smaller bluestones, and inside that free-standing trilithons. The whole thing aligns on sunrise at the summer solstice and sunset at the winter one. Building ran in phases from about 3100 BC to about 1600 BC, the great sarsen circle going up between 2600 and 2400 BC. It stands amid the densest concentration of Neolithic and Bronze Age monuments in England.