Garrett Carr travelled by foot and canoe along Ireland's border. Kapka Kassabova journeyed to what she calls "the edge of Europe". Frank Ledwidge's army career took him to the Balkans, Afghanistan and Iraq, Nikolas Ventourakis is fascinated by how to capture the abstract notion of borders in photographs. They talk to Anne McElvoy about the essence of edges, notions of the other and the challenges of invisible borders which come and go like the smile of the Cheshire Cat.

The Rule of the Land: Walking Ireland's Border by Garrett Carr looks at a landscape which has hosted smugglers, kings, runaways, soldiers, peacemakers, protesters and terrorists

Producer: Jacqueline Smith