@boffosock thanks for the book link. I will read into it, just came off a bit Eurocentric to me to claim one neolithic standing stone monument in UK was first. Maybe it is, but it sent my spidey senses tingling.

Always thought of Stonehendge as a burial ground with astronomical features (same as the pyramids this way)....

Not sure I would agree that an astronomical calendar isn't a mnemonic device. The entire point is to remind you "today is today or today is equinox" If calendar's are memory devices I don't know why I spend so much time failing to manage mine.