Athough it is clear that many still-existing religious locations were built on top of ancient pagan sites to "replace" the old beliefs, I am very sceptical about the idea of "lost knowledge" being carried forward by the moderns. How woud they know about it in the absence of records? We have no evidence of oral tradition, except in legend and mythology. After all, even the Hellenistic tradition of Gods is astronomical but came down to us as myth .
My own view is a straight-forward one. I think you had a people in ancient days - a small group of seafaring priests - who had some rudimentary mathematical knowledge and applied that knowledge to rudimentary astronomy and land survey. At some point in history, this knowledge was lost in northern Europe because that culture had no developed writing system and all that survived were ancient legends and myths, carried forward over millennia, e.g. in Ancient Britain, the tales of Merlin and King Arthur, which I am sure reach back to megalithic days.
I see my task to continue to try to prove how the ancients did their astronomically-based geodetic measurements and to get others interested in this quest.
Essentially we are talking here about the hermetic tradition - as on Earth, so in Heaven, or, more accurately, as in Heaven, so on Earth. In days before writing, you could not go down to the local store and buy maps. Still, people had to be able to get around on land and to navigate by sea. Hence, the ancients took a "fixed known map" - the map of the heavens, which was not only freely available but in ancient days probably known by most everyone - and then used that map - projected on the Earth - as a model for mapping the Earth below. Anyone having knowledge of the heavenly stars could thus find his way around on Earth by means of the megaliths, which served both as boundaries and landmarks.
We find the following written about Hermes at Gnosis.org :
"The name Hermes appears to have originated in the word for "stone heap." Probably since prehistoric times there existed in Crete and in other Greek regions a custom or erecting a herma or hermaion consisting of an upright stone surrounded at its base by a heap of smaller stones. Such monuments were used to serve as boundaries or as landmarks for wayfarers."
In Gaelic tradition it is known that heavenly locations had their earthly counterparts, although this knowledge is now submerged in Gaelic myth.
When I view the megaliths, the hermetic explanation is the only logical explanation for the existence of the most ancient megalithic sites, and I am very surprised that mainstream scientists "don't get it". The archaeologists are too busy digging up old pots (their principle seems to be that truth is only found underground) and the telescope-spoiled astronomers involved with the history of astronomy summarily reject anything which takes away from the glamour of modern astrophysics (as if modern astronomers seem to fail to understand that everything, including astronomy and physics, had humble origins, and that the origins of astronomy were inextricably tied in with what we today might call horoscopy or astrology). Both camps prefer overly modern convoluted, complex explanations for things which in my view were quite simple in ancient times.