Correction Appended

NAPOLEON said that if the world were a single state then its capital would be Constantinople. Even today, amid the traffic-choked streets of modern Istanbul , among the high-rises, the steep alleys and the glowing ancient churches and mosques, you can still feel exactly what he meant.

The air is thick with centuries of civilization, hallowed by history. Above the Golden Horn, once the wealthiest stretch of water on earth, hovers Hagia Sofia, perhaps the most beautiful church on earth, built in A.D. 537 by the Byzantine emperor Justinian with a dome so broad it was not superseded for a thousand years, until St. Peter's in Rome. Just a quarter-mile away floats its rival, the Blue Mosque, finished in 1616, after the city had fallen to the Muslim Turks. Islam and Christendom; East and West; Asia and Europe : the clichés are true, they do all meet here, and have brewed up an atmosphere unmatched on the planet.

As you'd expect in the capital of the world, there are restaurants from all over. But I didn't come to Turkey to eat Chinese, Italian or Russian. Cognoscenti say that Turkish is the best of the eastern Mediterranean cuisines, so I sallied forth in search of the most interesting indigenous kitchens.

As a visitor to Istanbul, you're sure to be sent to Kumkapi, a district packed with fish restaurants. In fact, it's nothing but fish restaurants, and by night it's busy, frantic, overwhelming - a bit like wandering into a cross between a hotel theme-night party and a 70's disco. Bright lamps, waterfalls of fairy lights, zithers and tambourines raging up and down the little pedestrian streets, amid terrace after terrace of outdoor tables - it gives new meaning to the word garish. Vendors stroll around selling everything you might need: Cohibas, dolls, teddy bears, and I even saw one man with a giant tin sailing ship hoisted on his shoulder.

With the Bosphorus, the Sea of Marmara, the Black Sea and the Aegean all within a morning's drive, Istanbul is a great city for fish. But more interesting than any place in Kumkapi is Tarihi Karakoy Balikcisi in the Karakoy district.

Finding the restaurant, however, just behind the fish market near the Galata Bridge, is anything but simple. Down an alley lined with hardware stalls, past 200 yards of screws, drills and hinges, all that gives it away is a wood-framed doorway and a little display window with a small sample of the day's catch. Everything here is of the day. When they run out they close. And it's lunch-only, consisting of two tiny upstairs rooms and an even tinier one downstairs. You can't make a reservation, although you can reserve a particular fish if it's in ("Hold the sole, we're on our way"). Choices go up on a blackboard.

Its owner, Hakan Ozkaraman, owner also of a ball-bearing store round the corner, is passionate about fish. "I'm amateur - this is the special thing," he said, raising a finger. "Here, just I am selling fish. Not ambience, not view, not fancy plates - just fish."