The fact that they're 20-50 meters in diameter could mean dwellings of some sort. And larger kite-based structures something of religious significance.
Otherwise, they could have indicated a route. I remember when I was hiking in Chile, finding any sort of stone arrangement that indicated some other person had been on this path always made me feel better. I usually look for signs anywhere I hiked, but I was alone in Chile and it got hairy for a bit.
The stones might have been the foundations of some old building/structure/dwelling.
The bulk of the structure might have been made of more perishable material like wood and straw and they disappeared over time, leaving only the foundation stones.
They range from early Bronze Age to Roman period, up until the 7th century. One or more has openings and a size similar to local ruins of a Roman fort. Others are oblong, closed shapes with spokes running to the center reminiscent of prayer circuits. One article mentioned that a few circles looked like a few that were in the still untranslated Voynich manuscript.