Why did London have to wait so long for a main line railway beneath its streets? For a few years in the mid-nineteenth century, Isambard Kingdom Brunel's broad gauge Great Western trains ran from Reading to Faringdon. Now, after many false starts, his vision is being realised as the Elizabeth Line carries passengers from Reading to the City once again and beyond Essex to Kent, using engineering that would have earned the admiration of the greatest Victorian engineers. London historian Stephen Halliday presents an engaging discussion of the fascinating origins and heroic engineering that made it all possible.