Built upon seven hills, Istanbul, like Rome, is one of the most ancient cities in the world, filled with splendor and contrast. It is an exotic place, so different from the ordinary that the casual tourist is likely to see at first only the contrast and the ugliness of narrow streets lined with haphazard houses. At the moment, many of these are being pulled down. Whole blocks are disappearing and more are scheduled to vanish to make room for wide boulevards that will show off its treasures to better advantage -- the great domes and graceful spires of its mosques, the panorama of the Bosphorus and the Golden Horn. Even when they are finished, however, the contrast will remain, for Istanbul is the only city in the world that is built upon two continents. For almost 3,000 years Europe and Asia have rubbed shoulders in its streets. Founded in the Ninth Century B.C. it was called Byzantium 200 years later when Byzas, ruler of the Megarians, expanded the settlement and named it after himself. About a thousand years after that, when the Roman Empire was divided, it became capital of the Eastern section. On May 11,330, A.D.,, its name was changed again, this time to Constantinople after its emperor, Constantine. In 1453 when the last vestige of ancient Roman power fell to the Turks, the city officially shifted religions -- although the Patriarch, or Pope, of the Orthodox Church continued to live there, and still does -- and became the capital of the Ottoman Empire. When that was broken up after the First World War, its name was changed once more. Rich in Christian and Moslem art, Istanbul is today a fascinating museum of East and West that recently became a seaside resort as well with the development of new beaches on the Bosphorus and the Sea of Marmara only a short distance from the center of town. Easy to get to, and becoming more popular every year, it is only fourteen hours from New York by Pan American World Airways jet, four hours from Rome. Start of tour Most of the sights lie in the old section across the Golden Horn from the modern hotels. I started my tour of them at the Turkish Government Tourist Office, next to Pan American's office on the left as you enter the driveway that leads to the Hilton Hotel. From there I turned left along Cumhuriyet Cadesi past more hotels and a park on the left, Republic Gardens, and came in a few moments to Taksim Square, one of the hubs of the city, with the Monument of the Republic, erected in 1928, in its center. Directly across from the Gardens I found a bus stop sign for T 4 and rode it down to the Bosphorus, with the sports center on my left just before I reached the water and the entrance to Dolmabahce Palace immediately after that. There the bus turned right along the Bosphorus, past ocean liners at anchor, to Galata Bridge over the entrance to the Golden Horn, a brown sweep of water that empties into the Bosphorus. Across the bridge on the left I saw St. Sophia with its sturdy brown minarets and to the right of them the slenderer spires of the Blue Mosque. On the other side of the Golden Horn I rode through Eminonu Square, with Yeni Cami, or the New Mosque, which dates from the Seventeenth Century, just across from the entrance to the bridge. Passing it, the bus climbed a hill, with the covered spice bazaar on the right and Pandelli's, a famous and excellent restaurant, above it. At the top of the hill the buildings on the left gave way to a park. I got off there, crossed the street, walked ahead with St. Sophia on my left, the Blue Mosque on my right, and in a moment came to the entrance of St. Sophia. Erected on the site of pagan temples and three previous St. Sophias, the first of which was begun by Constantine, this fourth church was started by Justinian in 532 and completed twenty years later. On his first trip to the finished structure he boasted that he had built a temple grander than Solomon's in Jerusalem. A few years later the dome fell in. Nevertheless, it remained one of the most splendid churches of the Eastern Empire, where the Byzantine Emperors were crowned. After the Turks conquered the city in 1453 they converted it to a mosque, adding the stubby minarets. In the second half of the Sixteenth Century, Sinan, the great architect who is the Michelangelo of the East, designed the massive buttresses that now help support the dome. With the birth of the Turkish Republic after the First World War, St. Sophia became a museum, and the ancient mosaics, which were plastered over by the Moslems, whose religion forbids pictures in holy places, have been restored. Inside over the first door I saw one of these, which shows Constantine offering the city to the Virgin Mary and Justinian offering the temple. On the columns around the immense dome are round plaques with Arabic writing. The eight green columns, I learned, came from the Temple of Artemis at Ephesus, the others, red, from the Temple of the Sun at Heliopolis. Beneath the dome I saw the spot where the Byzantine Emperors were crowned, a bit of floor protected now by a wooden fence. Behind this is a minber or Moslem pulpit and near it a raised platform with golden grillwork, where the emperors and, after them, the sultans, sat. Directly opposite is the emperor's door, through which they entered the building. Outside St. Sophia I walked through the flower garden in front of it, with the Blue Mosque ahead on my left. Across the street on my right I saw the Hippodrome, now a park. It was laid out in 196 for chariot races and other public games. Statues and other monuments that stood there were stolen, mostly by the waves of Crusaders. At the beginning of the Hippodrome I saw the Kaiser's Fountain, an ugly octagonal building with a glass dome, built in 1895 by the German Emperor, and on my left, directly across from it, the tomb of Sultan Ahmet, who constructed the Blue Mosque, more properly known by his name. Just before coming to the mosque entrance I crossed the street, entered the Hippodrome, and walked ahead to the Obelisk of Theodosius, originally erected in Heliopolis in Egypt about 1,600 B.C. by Thutmose, who also built those now in New York, London and Rome at the Lateran. This one was set up here in 390 A.D. on a pedestal, the faces of which are carved with statues of the emperor and his family watching games in the Hippodrome, done so realistically that the obelisk itself is included in them. Beyond it I noted a small green column, about twelve feet below the present ground level -- the Serpentine Column, three entwined serpents, which once stood at the Temple of Apollo at Delphi, Greece. Near the end of the Hippodrome I came upon the Built Column, a truncated obelisk of blocks, all that remains of a monument that once rivalled the Colossus of Rhodes. Magnificent Mosque Retracing my steps to the Mosque of Sultan Ahmet, only one with six minarets, I entered the courtyard, with a gallery supported by pointed arches running around it and a fountain in the middle. One of the most beautiful buildings in Istanbul, it was constructed in the early years of the Seventeenth Century, with a huge central dome, two half domes that seem to cascade down from it, and smaller full domes around the gallery. The round minarets, tall and graceful, rise from rectangular bases and have three platforms from which the muezzin can chant his call to prayer. Inside, the walls are covered with blue and white tile, the floor with red and cream carpets. Back at the Kaiser's Fountain, I walked left to the streetcar stop and rode up the hill -- any car will do -- past the Column of Constantine, also known as the Burnt Column, at the top on my right. It stands in the middle of what was once the Forum of Constantine, who brought it from Rome. I stayed on the car for a few minutes until, turning right, it entered a huge square, Bayezit, with the Bayezit Mosque on the right and the gate to the university just beyond it. There I got off, crossed the square, and on the side directly opposite the gate found a good restaurant, hard to come by in this part of the city. Called the Marmara Gazinosu, it is on the third floor, with signs pointing the way there, and has a terrace overlooking the Sea of Marmara. After lunch, in the arcade on my left just before reaching the street I found a pastry shop that sells some of the best baklava -- a sweet, flaky cake -- in Istanbul. It's a great favorite of the university students, and I joined them there for dessert. Taking the streetcar back to Kaiser's Fountain, I walked ahead, then left down the street opposite St. Sophia and just beyond the corner came to a small, one-story building with a red-tile roof, which is the entrance to the Sunken Palace. Actually an underground cistern, its roof supported by rows and rows of pillars, it was built by Justinian in the Sixth Century to supply the palace with water. There is still water in it. I found it fairly depressing and emerged almost immediately. Outside I walked past the entrance to St. Sophia, turned left at the end of it, and continued toward a gate in the wall ahead. Just before reaching it I came to a grey and brown stone building that looks somewhat like an Oriental pagoda, with Arabic lettering in gold and colored tile decorations -- the Fountain of Sultan Ahmet. Going through the Imperial Gate in the wall, I entered the grounds of Topkapi Palace, home of the Sultans and nerve center of the vast Ottoman Empire, and walked along a road toward another gate in the distance, past the Church of St. Irene, completed by Constantine in 330 A.D. on my left, and then, just outside the second gate, I saw a spring with a tap in the wall on my right -- the Executioner's Spring, where he washed his hands and his sword after beheading his victims. Passing through the gate, with towers on either side once used as prisons, I entered a huge square surrounded by buildings, and on the wall to my right found a general plan of the grounds, with explanations in English for each building. There are a good many of them. At one time about 10,000 people lived there. Following arrowed signs, I veered right toward the former kitchens, complete with chimneys, which now house one of the world's greatest collections of Chinese porcelain and a fabulous array of silver dinner services. Next to it is a copper section, with cooking utensils and a figure of the chief cook in an elaborate, floor-length robe. In the court once more, I went right toward the Reception House, a long one-story building with a deep portico. Going through a door into another small court, I had the Throne Room directly in front. I walked to the right around it to buildings containing illuminated manuscripts and came to the Treasury, which houses such things as coffee cups covered with diamonds, jewelled swords, rifles glittering with diamonds and huge divan-like thrones as large as small beds, on which the sultans sat cross-legged. They are made of gold and covered with emeralds, pearls and other jewels. Taking the path behind the Throne Room to the building directly beyond it, the Portrait Gallery, I went right at the end of it, through a garden to a small building at the back -- a sitting room furnished with low blue divans, its floor covered with carpets, its ceiling painted with gold squares and floral designs.