Accurate timekeeping is at the very root of all of the technological advances in the modern world, but how did it all begin? From Roman sundials to medieval water-clocks, people of all cultures have made and used clocks for thousands of years. Dan speaks to horologist, historian and former curator of timekeeping at the Royal Observatory Greenwich, David Rooney, about the importance of time, and what clocks can tell us about the history of human civilisation. David’s book, About Time: A History of Civilisation in Twelve Clocks, is out now.