Smuggling was a thing back then, right? Paying someone to help you navigate the not so hospitable and easy-to-get-lost-in deserts and forests.

Yes, to keep the invaders out. That’s border control, no? To control the flow of people between borders, military or otherwise, is border control. To control borders.

May I introduce to you the wall? There’s a whole wonder of the world that’s a wall: a Great one in China.

Also, there used to be people on those walls with pokey things that hurt. People outside the empire/nation/whatever they called it back then didn’t want to go near it when they weren’t supposed to, since they didn’t want to be poked by the pokey things.

With the invention of firearms, you can shoot a tiny pokey thing really fast! Pokey things have really advanced over the years, for the better or worse.