What else was there to do? There was no Internet, no television, no football (perhaps), no books, no broadcast radio.

I'm only half joking.

Maybe someone was "visiting" Scotland, and decided that it would look good in their backyard

Yea, ancients had a certain taste for decorations.

For example in Assyria, to get an audience with their king Ashurbanipal, I believe, one had to go through a corridor full of heads of king's defeated enemies.

We often forget how violent past was. It was extremely hard to live to adulthood without killing anyone.

See also: Stone of Scone.

Fascinating but also a lot more portable