You sunk my battleship!
Cribbage board.
Counting, groups of something. Three, five, seven, eight. Seven circled. Chiseled in stone, not exactly easy to do then or now. On a high hill.
Astronomical observation, rudimentary calendar. Balanced stone marks some significant sun, moon or star position from a particular vantage point.
We know many if not most ancient people practiced some form of astronomy, some were highly accomplished. That’s what this likely is, imho.