Ancient literary critics have set down certain rules for imaginative treatments of historical episodes: they must be based on historical fact; the imagined episodes and motivation must be "such as might likely have happened" (Aristotle would say they must be truer than actual history), and the whole must be instructive and edifying. Marguerite Yourcenar has not only observed these rules in her book, "Hadrian's Memoirs," but has also followed a favorite ancient practice in putting her reconstruction in the form of an epistle, addressed by Hadrian to his adoptive grandson and eventual successor, Marcus Aurelius. The excellence of her product proves the wisdom of the ancients.

Even a reader indifferent to history and historical personages must find the Hadrian here presented a full and sensitive man well worth knowing. The early pages in which the prospect of imminent death leads him to savor the experiences and sensations of...