Visualize an ancient Egyptian pharaoh by his pyramid. Now imagine Caesar and the Roman Forum. Now a Viking longship with its raiding party. And now conjure up Constantinople in its heyday, as the emperor, escorted by his most trusted logothetes, greets a company of cataphracts just returned from battle.

Unless you're a scholar, that last historical vignette is probably not calling much to mind -- no stirring visions, I'll bet, of a purple-clad monarch attended by a flock of long-robed civil servants and triumphant heavy cavalry.

And this is strange, considering that Constantinople had one of the most important empires in Western history, lasting more than a millennium and deeply affecting every culture that ran into it, from Swedish vikings to Muslim Turks.

A stunning exhibition now at the Metropolitan Museum in New York, called "Byzantium: Faith and Power (1261-1557)," may go some way toward restoring the culture of Constantinople to the popular imagination. More than 350 artworks and artifacts, many of them masterpieces rarely on public view, have been flown in from churches and museums in 25 countries. Even the desert monastery of St. Catherine in Sinai, founded from Constantinople 1,500 years ago, sent over a roomful of its greatest treasures. This is one of those shows that you feel privileged to attend, because you're sure you'll never see its like again.

The exhibition is the last in a series of three Byzantine surveys that the Met launched back in 1977. It picks up the story in the later 13th century, when the empire based in Constantinople was already on its last legs. The city had been founded in A.D. 330 by the newly baptized Roman Emperor Constantine, on the strategic site of modern Istanbul, where Europe and Asia meet. The entirely Christian, Greek-speaking capital was intended as a counterpart and counterpoise to the old Latin-speaking capital that survived in Rome. And long after Rome and its western European holdings fell to the Goths and Franks and Saxons, the Eastern Roman Empire lived on and often prospered. Shrinking and expanding across Asia Minor, Greece, the Balkans and the Middle East, with toeholds sometimes even farther west, it endured until its final conquest by the Ottoman Turks in 1453.

Though renamed "Byzantium" by a 16th-century scholar (he liked the word's Greek ring), Constantinople and its possessions had been ruled by people who always referred to themselves simply as Romans. They thought of themselves, correctly, as the direct political and cultural descendants of classical antiquity.

In its last 200 years, Constantinople lost almost all its holdings to incursions from the Slavic north, the Muslim east and the Latin west. From 1204 to 1261, the capital itself had been held by European "crusaders," sidetracked on their way to Palestine by the prospect of the ancient city's loot. The works now at the Met were all made after the exiled Byzantine nobility retook the city and a bare few disconnected parcels of its former lands in Greece and Asia Minor. And still Byzantium, now an empire in name alone, had a level of culture that stronger, younger rivals could be jealous of.

The Met has on display a huge trove of religious icons -- many much bigger and grander than the term usually suggests -- that show just how vibrant late Byzantine art could be. Whether made in Constantinople itself or for the Orthodox Christian churches founded under Byzantine influence in Greece, Russia, Serbia, Bulgaria and the Near East, these paintings are full of creative energy and innovation. They experiment constantly with how a picture can be put together, with how theology can be rendered in paint, with how a sacred story can be told. It's as though all the energies the Byzantines had once put into conquering, ruling and defending land now went into building culture -- the last domain they could control.

Looking back from our time, long after the radical realism of the Italian Renaissance has become old hat, it's easy to see Byzantine icons as stiff and staring, with an almost primitive religious intensity. A catalogue essay by an archbishop in the Greek Orthodox Church, where such icons are still used, gives that standard modern view of them. They're different from the last 600 years of naturalistic Western art because they're about the spirit, not the flesh. But when these pictures were first made they must have seemed on naturalism's flashy cutting edge: Byzantine artists of the 13th century went further in the depiction of light, form, space, the human body and emotion than anyone in the West had done for centuries. The Renaissance in Italian art came about in part under the influence of an earlier renaissance in Byzantine art that this show explores.

And even those fantastic icons don't capture the simple extravagance of Byzantine culture. I dare anyone to claim that the works in precious metals or exquisitely embroidered silks on show at the Met are the products of a culture less concerned with this world than the next. When a craftsman assembles thousands of tiny grains of glass and gold and marble into a micro-mosaic of a warrior Saint George on his white horse, his absurd labor may imply a tribute to God. But it must also be meant to show off a patron's wealth and taste, as well as the artist's amazing hand and eye.

It's easy to see why, even in the empire's dying days, the culture of Byzantium reached so much farther than its might. The Met's survey should help it reach out right to us.

Byzantium: Faith and Power runs through July 4 at the Metropolitan Museum of Art in New York. For information, call 212-535-7710 or visit www.metmuseum.org.

The lid of an early 15th-century silver reliquary lauding the four martyrs of Trebizond, the last Byzantine city to fall to the Turks, on view at the Metropolitan Museum of Art. An eight-inch mosaic medallion from the early 14th century shows Saint George slaying the dragon.From Washington's Dumbarton Oaks collection, a 13th-century mosaic icon showing the 40 martyrs of Sebasteia -- Roman soldiers left to die on a frozen lake if they did not renounce their Christian faith.An icon of the Annunciation, made in Constantinople in the early 14th century. Crisp architectural space, softly modeled faces and emotion modestly expressed -- is this the cradle of Renaissance realism?A 14th-century robe or sakkos, in silk and silver thread, worn on feast days by Constantinople's highest clerics. It marks a high point in Byzantine embroidery, which could surpass even painting in its ability to represent a sacred scene. It was long (and erroneously) known as the dalmatic of Charlemagne.The "Holy Face of Laon," a Slavic icon that ended up in northern France in 1249, is a famous Byzantine image based on a face cloth said to have been imprinted by Jesus with his likeness. The Slavonic inscription translates as "The face of the Lord on the handkerchief." Two Russian holy martyrs, the saints Boris and Gleb, as depicted on a mid-14th-century icon from Moscow.