When you see rock walls around fields, it's often partly to dispose of unwanted rocks in the fields. “This is an awesome amount of manual labor, but it is trivial when compared to the much larger effort of getting stones to the edges of the fields in the first place.”[1]

An extreme case is western Ireland. Tiny plots surrounded by far too many stone walls. Pretty, but too rocky for sustenance farming. Cromwell ordered the Catholics to go "to hell or to Connacht".

[1] https://www.earthmagazine.org/article/history-science-and-po...