My neck of the woods are littered with glacial erratics. Some are in the middle of broad, alluvial rich river valleys, some sit atop hills and mountains. It would make sense to use a glacial erratic that was already sitting atop a small rise on a plain. It would stick out like a sore thumb for nomadic hunters as a landmark, gathering place. Wouldn’t take long for some to get a belly fully of elk and a little bit of fermented juice and then next thing you know Thog says, “Hey, hold my leather flask. Watch this.” And soon it’s a drunken project.
:’) The large ‘sarsen’ stones at Stonehenge were clearly carved under the supervision of a Type A personality. One of the lintel stones was begun on the ‘wrong’ side, and the big boss — whomever it was — made the workers change it, do it ‘right’. The problem was, they were partly done on the ‘wrong’ side, and there mistake survives.
Many more sites all over the place:
https://www.pinterest.com/JudithZiyal/megaliths-dolmen-menhirs-hunebedden/
Castlerigg, for instance:
https://en.wikipedia.org/wiki/File:CastleriggStoneCircle(SimonLedingham)Jul2005.jpg
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