In 49 BC the Rubicon river was a clearly defined border between Cisalpine Gaul and Italy itself. Crossing the river was such a momentus decision that we now have the phrase “Crossing the Rubicon” to mean making a decision that you can’t go back on. So, borders have been clearly defined for at least 2000 years.
Borders weren’t even loosely defined.
In 49 BC the Rubicon river was a clearly defined border between Cisalpine Gaul and Italy itself. Crossing the river was such a momentus decision that we now have the phrase “Crossing the Rubicon” to mean making a decision that you can’t go back on. So, borders have been clearly defined for at least 2000 years.