This book tells the story of our greatest invention. Or, it almost does. Almost, because while the story has a beginning – in fact, it has many beginnings, not only in Mesopotamia, 3,100 years before the birth of Christ, but also in China, Egypt and Central America – and it certainly has a middle, one that snakes through the painted petroglyphs of Easter Island, through the great machines of empires and across the desks of inspired, brilliant scholars, the end of the story remains to be written.