By Nicholas Guild

Atheneum. 552 pp. $21.95

"In this city," the narrator/hero of "The Assyrian" remarks, "half the inhabitants earn their bread by spying on the other half." That may sound like Washington in the 1980s, but it is actually Nineveh, capital of the ancient Assyrian Empire, in the 7th century B.C. Perhaps we should let the narrator introduce himself; he does it with such resonance: "I am Tiglath Ashur, son of Sennacherib the Glorious, Terror of Nations, and my words ring with truth like silver coins."

How Tiglath was defrauded of his rightful crown and the hand of the woman he loved is the essential subject of "The Assyrian," a historical novel brimming with sex and violence, harem intrigues, witchcraft, poisons, institutionalized cruelty and dire prophecies that hang over Nineveh and Tiglath like storm clouds waiting to burst.

If we are to believe Tiglath's story (as told by Nicholas Guild), he was also, secretly, the father of Ashurbanipal, who brought the city and the empire to their peak of power and glory. Perhaps more important, he was the true choice of the god Ashur to succeed Sennacherib, although his mother was merely a Greek concubine, not one of the royal wives. Finally, he was, by his own account, a military genius, a master of tactical concepts at a time when war was still usually a loosely organized free-for-all.

Specifically, he claims credit for inventing the "hedgehog" defense for spear-bearing foot soldiers against cavalry, one of the revolutionary tactical inventions of antiquity and a predecessor of the classical phalanx. True or not, his account of its first use, and the surprise and consternation it brought to his enemies, is absorbing. In one episode after another, leading a relatively small, highly trained army, he triumphs over massive concentrations of undisciplined barbarians. The story is well told and should appeal to those who like to read of violence with subtle overtones in exotic settings.

Guild, whose best-known previous novels have been about modern espionage, slips easily into an archaic writing style and viewpoint, like that of ancient chronicles, for this first-person narration. The narrator's psychology is rudimentary but informed by experience and a subtle mind. His contempt for any civilization that is not his own does "ring with truth," but he seems atypical in some ways of Mesopotamian warriors of his time. He has a penchant for seeing the viewpoint of another person, even an enemy, that is rare at any time and must have been almost nonexistent in ancient Assyria. He also tends to idealize women (or at least one woman) in a way that would have seemed odd in his society, where women's flesh was a commodity to be bought, traded or won in battle.

His inclination to mercy for some of his enemies -- his knack for turning defeated foes into allies rather than corpses -- also contrasts curiously with the usual practices of his era. One of the book's recurring diversions is the colorful description of drastic ways in which kings punished their enemies -- roasting them, boiling them or skinning them alive, preferably at large, festive public gatherings.

In the novel as in history, the successor to Sennacherib is his son Esarhaddon, who was king of Assyria from 680 to 669 B.C. As Tiglath tells it, he and Esarhaddon grew up together, first in the harem and later in the barracks for young military officers, neither dreaming that he might be eligible for the crown. In the background constantly lurks the shadowy figure of the Lady Naq'ia, Esarhaddon's mother, plotting to bring her son -- and thereby herself -- to the supreme power. People who stand as obstacles to her ambition are eliminated in subtle, mysterious, often deadly ways; Tiglath himself survives several assassination attempts, guessing who is behind them but unable to act against her.

Among Guild's best passages are those that describe Esarhaddon's gradual transformation from a carefree warrior into a troubled monarch -- almost an Assyrian Macbeth -- desperately clinging to a crown that he does not really want or deserve and trying to convince himself that his mother's will is really his own. The gradual destruction of the boyhood friendship between Tiglath and Esarhaddon is a major theme, as is the destruction of Babylon by Sennacherib. Guild (or Tiglath) traces in minute detail how the city's resistance was worn down by attrition, plague and starvation, then the massacre of the few feeble survivors of the siege, the leveling of every building in the metropolis and the diversion of the course of the Euphrates to remove all traces of the great city. Limiting himself to the idioms of that ancient world, Guild manages to imbue his tale with traces of tragic grandeur.

The reviewer is the music critic of The Washington Post.