It is not often that a book’s blurb gives any idea of what’s inside, but Helen Castor’s endorsement — ‘a masterclass in the practice of history’ — is as good a description of this brilliant new biography of Charlemagne as we are likely to get.

The broader contours of the life will be familiar to many readers, but what we have here — pace Janet Nelson — is less the ‘old-fashioned’ biography that she claims but a wonderfully generous sharing of knowledge that combines the conversational tones of the ideal classroom with the intensity of the trained anatomist, poised, knife in...