I have been reading J.M. Coetzee’s novel “Waiting for the Barbarians.” It concerns a magistrate, a servant of Empire , stationed on a remote frontier, who watches with mounting indignation as fear of barbarian encroachment is used to justify a brutal and self-defeating imperial campaign of violence and torture. It is a portrait of an aging man, stung by his conscience, bewildered by his times.

In one passage, Coetzee writes: “Every year the lake-water grows a little more salty. There is a simple explanation — never mind what it is. The barbarians know this fact. At this very moment they are saying to themselves, ‘Be patient, one of these days their crops will start withering from the salt, they will not be able to feed themselves, they will have to go.’ That is what they are thinking. That they will outlast us.”

Barbarians come in different guises. Coetzee’s novel turns in part on the fact that the barbaric presence in his pages is the Empire, not the Empire’s imagined enemies. It is of the nature of declining powers to imagine foes, to flail, to produce zealots, to embark on doomed wars, to flex the atrophying muscles of dominance. It is of the nature of life that imagined enemies, once provoked, turn into real ones.

On horseback, ragged mirages in the dust, Coetzee’s barbarians do not really need to do anything. Hardly more than chimera, they suck the Empire into their labyrinth. This is because the Empire is dying, just as the magistrate is dying. He is an aging libertine with an agile mind and a love of knowledge — a speck, as he sees with unforgiving insistence, on history’s tide. This is a novel about the desperation of mortality.