A narrative history of the men and women who have explored Mars and mapped its surface from afar, and in so doing conditioned our understanding of our nearest planetary neighbour. Mars is the most observed and imagined place that humans have never been. Human names glitter on its surface, commemorating astronomers and physicists. Classical mythological identities have been stamped on its most prominent geographical features. Oliver Moreton examines how the process of exploration in space, of mapping, conditions what we discover there. Hence our understanding of the surface features of Mars is in part a product of the fact that a specialist in water movement and its erosion comes from Malham and sees on Mars a version of the limestone Yorkshire cliffs. Our appreciation of Mars, made possible by ever more powerful telescopes and digitized signals, has increased far ahead of our ability to fulfil the benefits of all the Mars-gazing. But in our imaginations we have all but colonized the red planet: the work of Arthur C. Clarke, Ray Bradbury and Kim Stanley Robinson has filled the landscape with human potential. Olympus Mons, Mars' biggest volcano is more than three times the height of Everest and contains enough rock to cover the whole of Texas in a layer five miles deep. It's that sense of awe that has gripped the troupe of researchers and astronomers who have held their sights firmly on Mars.