No matter where you turn, it seems that the taut lines of borders are vibrating to - or even calling - the tune of global events. Today, there are more borders in the world than ever before in human history. Beginning with the earliest known example, Crawford travels to many borders old and new: from a melting glacial landscape to the conflict-torn West Bank and the fault-lines of the US/Mexico border. He follows the story of borders into our fragile and uncertain future - towards the virtual frontiers of the internet and the shifting geography of a world beset by climate change.

As nationalism, climate change, globalisation, technology and mass migration all collide with ever-hardening borders, something has to give. And Crawford asks, is it time to let go of the lines that divide us?