[pavel_lishin]

Fences aren't about privacy, fences are^ about property rights and defense.

^ mostly, yes, you can find exceptions even back in pre-history.

[ddebernardy]

Citation please? (I couldn't find any.)

[yareally]

History of fences on Wikipedia talks about it dating back to at least feudal times when discussing property rights and boundaries. Obviously much farther back when discussing defensive use cases (Hadrian's Wall and The Great Wall being two massive examples I can think of quickly).

https://en.wikipedia.org/wiki/Fence#History

Not the first case of fence use in property rights, but barbed wire was first invented to keep property in (animals) more so than keeping others out.