Stonehenge is a henge constructed from massive stones.
The function is as an astronomical observatory to tell time
The precession of the earth’s axis and rotation are the only time constants to be reliable year after year after decade
In America, years later, the residents at the city of Cahokia built a wood henge that was correlated with the various permanent mounds to accurately tell time. At the time it was built, Cahokia was more populous than London
Food was better, too. Beer, not as good.