Rome — I am sitting on the steps of the Capitoline Hill, as close as I can approximate the spot where, exactly 250 years ago today, on October 15, 1764, the 27-year old Edward Gibbon was struck by the muses, leading to perhaps the greatest work of historical scholarship in the English language. Though the anecdote in his biography recalling the moment has been called into question, it is both sufficiently famous and sufficiently inspiring to anyone with a historical bent to warrant retelling. Gibbon’s recollects the moment: It was at Rome, on the fifteenth of October, 1764, as...