BOOK REVIEW / NONFICTION : A Rich Tale of the Beginning and Its Thunderous End : BYZANTIUM: The Decline and Fall by John Julius Norwich; Alfred A. Knopf; $35, 488 pages

It was the early morning of May 29, 1453. The great walls of Constantinople were breached by the furious assaults by a quarter of a million Ottoman Turks, led by the 21-year-old Sultan Mehmet II. The 10,000 defenders under Emperor Constantine XI Paleologus melted away; he disappeared in the fighting. The allied Venetian and Genoese fleets fled.

The Turks--as all conquerors did in those days, Muslim and Christian alike--slaughtered, raped and pillaged, despoiling the great church of St. Sophia.

After 1,123 years and 18 days, New Rome, the Byzantine Empire, was at an end, and the Muslim Turks were firmly established in Europe.

To rescue the Byzantine Empire from its obscure and, for centuries, dismal reputation in the English-speaking world, John Julius Norwich in 1988 published his first of three volumes chronicling the empire from the founding of Constantinople by the first Emperor Constantine on May 11, 330, to its thunderous fall.

The first volume took the story to the crowning of Charlemagne in Rome as Roman emperor of the West in 800; the second, from there through the most creative years of the empire to its ominous defeat by the Seljuk Turks in 1071 at Manzikert in eastern Turkey, by which it lost three-quarters of its possessions in Asia Minor, never to regain them.

This third and last volume takes us from there to the heroic and tragic defense of a pitifully reduced once-great nation.

Norwich makes large claims for the eastern empire. It was, he writes, “a worthy successor” to the ancient civilizations of Greece and Rome.

It beat back two great threats from the east--Persia in the seventh century and the Caliph of Baghdad in the eighth.

“Were it not for that great oriental bastion of Christendom. . .” he asks, “what language would we be speaking today, and what god would we worship?”

When learning was all but extinguished in the Dark Ages of Western Europe, he argues, “it was on the banks of the Bosphorus that it continued to blaze, and that the old classical heritage was preserved.

“Much of that we know of antiquity--especially of Greek and Latin literature and of Roman law--would have been lost forever but for the scholars and scribes and copyists of Constantinople.”

Norwich is refreshingly not afraid to have strong opinions.

Of the “splendor” of Byzantine art, he writes: “Never in this history of Christianity--or, one is tempted to add, of any other of the world’s religions, has any school of artists contrived to infuse so deep a degree of spirituality into its work.”

But a careful reading of the three volumes makes the disapproval of Edward Gibbon and his successor historians understandable, if not entirely just.

All Christianity was given to ferocious theological disagreements; the Greeks of the Eastern Empire were especially disputatious. For centuries people who honored the cross slaughtered one another over bitter arguments about the exact relation of man to God in the person of Jesus Christ. Later the Holy Ghost was dragged into the controversy.

The spirit of moderation and toleration of the Antonine emperors that Gibbon so admired in “The Decline and Fall of the Roman Empire” perceptibly gave way over the centuries to hatred and monstrous cruelty. By the eighth century, eastern emperors were routinely slitting the noses of their rivals, even children; no maimed person could ever be emperor.

Castration became ordinary: eunuchs were thought to make excellent public servants on account of their lack of personal desire and ambition. The devious intrigue in the empire made Byzantine a common adjective.

In all this the emperor was raised ever higher in the eyes of his people until he came to be regarded as equal to the apostles, the “Vice-gerent,” as Norwich puts it, of God on Earth.

Norwich makes clear that he is no original historian. He works from published secondary works, not primary sources. He writes little of economy, for he is no economist. Nor does he write of “trends,” because he is no sociologist.

He is instead a teller of tales, and a good one. He quite frankly states that he favors those ancient chroniclers whose tales are lively, if perhaps not always true.

Norwich has a flair for the dramatic, and the large canvas. In this last volume, the arrival of the Crusades from a cruder Western Europe are especially well-done.

To the subjugation of Constantinople by the Fourth Crusaders led by the octogenarian Venetian Doge Enrico Dandolo, and the plunder of its treasures, including the four bronze horses sent to San Marco in Venice, Norwich gives a melancholy force.

A word on the book itself. All three volumes are examples of fine bookmaking.

The paper is rich; the type, clear; the margins, ample. In the third book there are six excellent maps, 20 fine color plates and 20 black-and-whites.

And for those who care to follow with exactitude the bewildering cast of characters, many of whom have the same or similar names, there are seven family trees of imperial families and their opponents. Each book has a complete index. These books, like the empire, were designed to last.