https://arkeonews.net/mysterious-mongolian-arc-in-eastern-mongolia-studied-for-the-first-time/
I'm no expert but my money is on something to do with horses 🐎!
Don't let your imagination gallop away with you, or put the horse before the cart ;) . As the authors of the study quoted in the article say, they really haven't much idea about it yet. Let them trot around a bit more to see what they can dig up.
Neigh lad
Maybe it's ritual?
Given the dates (11th-13th C), position (mostly along prefecture boundaries), and comments in the histories, the fortifications (likely as much customs barriers as defensive) probably date to the civil wars at the end of the Liao (1110-1130).
That's been the academic consensus for as long as I can remember.
Tom..