Begin your tour of the Sultanahmet district, the heart of old Istanbul, at Hagia Sophia. Built by the Emperor Justinian in the early 6th century A.D. and designed by Anthemius of Tralles and Isodore of Miletus, the church is one of the marvels of world architecture. Converted into a mosque in 1453, it is now a museum. Its massive dome still dominates the skyline of old Istanbul. It is also famed for its mosaics, including glittering portraits of emperors and empresses and a poignant Virgin and Child. Next, you will visit the Blue Mosque which takes its name from the exquisite tiles adorning its interior. Built by Sultan Ahmet I in the early 17th century and designed by a pupil of Sinan, the greatest of Ottoman architects, it is the only imperial mosque with six minarets. Its courtyard is especially grand. The Hippodrome, the stadium of ancient Byzantium, held 100,000 spectators and featured objects from all corners of the empire. Of these, an Egyptian obelisk and a bronze sculpture of three entwined serpents from Delphi survive. The Grand Bazaar was the commercial heart of the old city and its 4,000 shops are full of treasures including carpets and kilims, silks, jewelry, ceramics, icons and leather goods. Wandering through the Grand Bazaar, indulge in some shopping, Ottoman style. Enjoy your lunch at a rooftop restaurant with a view of the Bosphorus. Visit Topkapi Palace, the great palace of the Ottoman sultans from the 15th to the 19th centuries, housing an exquisite collection of precious gems, jewelry thrones of sultans, robes worn by the sultans and their families, miniatures, the Holy Mantle and the Chamber of Sacred Relics. (The harem is not included in the program and visit will require an extra entrance fee.) Last but by no means least, visit the New Mosque completed in 1665. Originally named Valide Sultan Mosque, the construction was ordered by Safiye Sultan, the wife of Sultan Murad III and the mother of his successor Sultan Mehmed III, hence the name Valide Sultan meaning Queen Mother. The mosque is an Imperial Mosque and one of the famous architectural landmarks of Istanbul.