Historically known as Constantinople, the city is located on both sides of the Bosporus Strait with the population of 12 million people. Istanbul served as the capital of the Roman, Byzantine and Ottoman Empires. Two city districts are located in the Asian part, the rest 25 — on the European. Main tourist attractions include Hagia Sophia, Blue Mosque located on the Sultanahmet Square and the Obelisk of Theodosius transported from the Upper Egypt; Basilica Cistern with well-preserved columns reuse blocks carved with the visage of Medusa and pool wishes, and tremendous bridges across the Golden Horn Bay. Besides the historical and cultural heritage, Istanbul is economical and scientific center of Turkey housing best universities, conservatories and libraries. Ordinary streets are full of bright colors with scarlet crowfeet, dark-blue sea and red cats stretching out on the motley carpets.