Borders are extremely important, both in terms of national sovereignty and for human mobility and limits to it. In nomadic societies people often moved relatively freely with the seasons over long distances but borders have become much more important with the evolution of nation states in the last few hundred years. Borders today are marked on maps and sometimes marked on the ground with border fences or even worse. They can function both to keep people out and, as with the Berlin Wall, to keep people in. Britain has distinct maritime borders but in many places, borders are disputed and there are border conflicts and restricted border crossings. We will return to questions about national borders in future episodes.