The Gateway to the East, Istanbul stands on both sides of the Bosphorus, an important natural waterway linking the Black Sea to the Mediterranean and separating Europe from Asia. There are two bridges across the Bosphorus and another is planned. This city, known as Byzantium and then Constantinople in ancient times, abounds with monumental architecture and traffic congestion. But it has two faces - European with its tree lined boulevards and chic cafes and shops - Eastern in the crowded backstreets and bazaars. It has two city centres, both on the European side, separated by the inlet known as the Golden Horn - the historical Sultanahmet and Taksim CBD.