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?