A City of Treasures, Istanbul Is Caught Between East and West

The splendors of Turkey's former capital are the inheritance of three great empires

BACK in the 17th century, Hazerfen Ahmet Celebi climbed to the top of the Galata Tower, then the highest structure in Istanbul. Strapping on a pair of homemade wings, he jumped from the tower and glided over the city. Townspeople went ballastic and hailed him as a hero.

Annoyed by all this publicity, the sultan sat and sulked.

Beware a sulking sultan.

Unable to cope with this bothersome attention-getter, His Majesty presented this Icarus wannabe with a bag of gold and his marching orders: Get out of town, pronto!

Today there are less frightening ways to see Istanbul -- unless, of course, you take a taxi.

The Galata Tower, built in 1348, still stands, and is still a fine way to get your bearings in this wondrous city that has one foot planted in Europe and the other in Asia. A rickety elevator will take you to the top, where all the splendors of the city are spread beneath you: the red stucco roofs that stretch away in all directions; the commercial ships that ply the blue waters of the Bosporus and Golden Horn; and the many ancient mosques that hulk like giant tortoises against the thick gray mist.

This former capital of Turkey is as much museum as city. It bulges at the seams with dramatic remnants of three great empires: Roman, Byzantine, and Ottoman.

The most important place to visit is in the old city, on the other side of the Golden Horn. This means, (gulp) taking a cab. There are some 17,000 yellow-and-black ''taksi'' that buzz around this city, so you won't have trouble finding one. Just sit back and shut your eyes until you arrive at your destination.

Now open your eyes, for there in front of you is the most famous building in the old city -- at least to the Western world -- the Haghia Sophia, one of the most extraordinary buildings in the history of architecture.

Still a remarkable edifice, it must have been even more so when it was commissioned by Emperor Justinian I in the 6th century. Christened as the Church of the Divine Wisdom, its interior space and dome are staggering. It was the world's largest domed structure until the building of St. Peter's in Rome.

So impressed was Sultan Mehmet II when he captured the city from its Christian defenders in May 1453 that he converted the church into a mosque the same week, rather than destroy it. On its way to mosquedom, exquisite mosaics depicting the life of the holy family were plastered over and four minarets were constructed. In 1934 the church- cum-mosque reopened as a museum, its remaining mosaics again exposed.

Standing defiantly across a small park from the Haghia Sophia is arguably the most beautiful structure in Istanbul: the Sultan Ahmet Mosque. Completed in 1616, it's the height of Ottoman grace and splendor with its great dome, cascading semidomes, and six pencil-slim minarets that punctuate the sky. It's popularly called the Blue Mosque because of the blue-and-white Iznik tiles in arabesque and floral patterns that decorate its interior columns and domes. It can house some 6,000 faithful Muslims as they pray barefoot on layers of antique Turkish carpets.

The Blue Mosque was the centerpiece of a complex of buildings that included a market, hospital, kitchen, library, school, and cemetery.

Before the short walk to Topkapi Palace, you may want to cool off with a tour of the Yerebatan Saray (Sunken Palace) a vast, cavernous underground cistern dating to the 4th century. Here you descend well below street level to a watery world where some 335 columns, some with Corinthian capitals, were brought from ancient Greece, Syria, and surrounding lands to support the brick-vaulted ceiling. Thousands of tons of muck were dredged from this cavern in 1987. The chamber is now home to schools of carp and a cool respite for tourists. It has an eerie, dark coolness, like a stage set from ''Phantom of the Opera.'' In fact, the play was to be performed here until the plug was pulled by the Department of Antiquities. Concerts are held here on occasion.

Returning to the light of day, walk to Topkapi Palace, scene of much intrigue during the 15th to 19th centuries, when the ruling sultans called it home. The harem tour is the most popular. Entering through the side gates and quarters of the Black Eunuchs who guarded the complex, shuffle through the audience hall, a few of the more than 400 bedrooms, and the hamam (Turkish bath).

No one leaves without visiting the Imperial Treasury where the bounty of the Ottoman past is kept. Emeralds are the jewel of choice here, and the collection is vast. By the hundreds, they stud the wide gold throne on which the sultans held court. Three emeralds the size of plums are mounted in the golden Topkapi Dagger, a nonspeaking star of the 1964 movie ''Topkapi.'' In another room the fabled Spoonmaker's Diamond -- fifth largest in the world -- sits illuminated on a rocking pedestal, flashing its facets to a flock of gawking tourists.

But for all of Topkapi's treasures, the real one is this remarkable city. Caught between East and West, draped in a pale-blue smog, it stands ready to assault the senses, the emotions, and the mind.