I have been making the best of lockdown by reading properly, from start to finish, Edward Gibbon’s Decline and Fall of the Roman Empire, in a seven-volume edition that is less daunting than it sounds, when you consider how addictive his rolling prose is. I have just reached the point, near the end of the great work, where Gibbon describes the sack of Constantinople by the armies of the Fourth Crusade in 1204.