It's been a while since I took the class, but I think E. C.
Krupp's 'In Search of Ancient Astronomies' gives a fairly
detailed investigation of Stonehenge (and other stone and wood
circles of Europe and North America). His conclusion is that
they were all calendars, of sorts; one characteristic all of the
circles have in common is a means of noting the date of the
solstices and equinoxes.
My own opinion is that Stonehenge was an early attempt to build
a baseball stadium.
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