[defrost]

There are many possibilities here.

Look up "glacial erratic", these are stones often as large as cars that are frequently found in lines, carried forward by glaciers, dropped as ice retreats.

People are, believe it or not, intelligent enough to infill really big rocks with smaller rocks and other materials in order to create a race wall to funnel herds towards a blind for corralling or killing - it's still done to this day albeit with dogs, horses, bikes, and other vehicles.

Depending on the landscape these may also be walls resulting from clearing rocks to surround herd animals and clear soil for more feed growth - again, path of least resistance dictates infilling between big rocks.

Various parts of Europe are littered with examples of very old rock walls, a kilometre or so is not much by comparison.