Starting with a drive around the Golden Horn and the great walls of Constantinople, we pass Dolmabahce Palace, then cross the Galata Bridge before arriving in Sultanahmet Square, where we visit. We begin our tour of the Sultanahmet district, the heart of old Istanbul, at Hagia Sophia*. Built by the Emperor Justinian in the early 6th century AD 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 Chil