I think it's an omphalos or baetylus - a remnant of ancient pagan sky worship. Same as the black rock.
Omphalos:
An omphalos (ὀμφαλός) is a religious stone artifact, or baetylus. In Greek, the word omphalos means "navel". In Greek lore, Zeus sent two eagles across the world to meet at its center, the "navel" of the world.[1] Omphalos stones marking the centre were erected in several places about the Mediterranean Sea; the most famous of those was at Delphi. Omphalos is also the name of the stone given to Cronus. In the ancient world of the Mediterranean, it was a powerful religious symbol.
Baetylus:
Baetylus (also Bethel, or Betyl) is a word denoting a sacred stone, which was supposedly endowed with life. According to ancient sources, these objects of worship were meteorites, which were dedicated to the gods or revered as symbols of the gods themselves. An example is also mentioned at Bethel in Genesis 28:11-19.
The Roman-Era Midrash Tanchuma sums up the centrality of and holiness of this site in Judaism:
As the navel is set in the centre of the human body,
so is the land of Israel the navel of the world...
situated in the centre of the world,
and Jerusalem in the centre of the land of Israel,
and the sanctuary in the centre of Jerusalem,
and the holy place in the centre of the sanctuary,
and the ark in the centre of the holy place,
and the Foundation Stone before the holy place,
because from it the world was founded.
These things are not unique to the Abrahamic religions and are found all across the pagan world. My personal opinion/theory is that the gods = constellations, planets, the moon, sun, etc. and these omphalos' or baetylus' were originally moved around following the movement of constellations or individual stars over the years. They were said to be the "physical representation of the gods on earth" and they would move them around, worship them, organize festivals around them, etc. I wonder if any of them happen to be astronomically aligned to specific constellations or individual stars or align with them during a specific time of the year?
The ancient Egyptian calendar, for example, used the heliacal rising of the star Sirius to mark the beginning of their year. Other cultures used different lunar phases, solar phases, constellations, etc. to determine their calendars and they used it all to help them with agriculture, harvesting, and so on.
Maybe these ancient stones were used as calendars or something. Take a look at lunisolar calendars and their relationship to constellations to see what I mean.