Istanbul is a megacity in Turkey -- the fifth largest in the world -- and it stands on both sides of the Bosphorus Strait that runs between the Aegean Sea and the Black Sea and constitutes the border between Europe and Asia. During the eras of the Byzantine and Ottoman empires, Istanbul was known as Byzantium and then Constantinople. Lisbon is the capital and largest city of Portugal.
The two cities are situated roughly at the far southwestern (Lisbon) and southeastern (Istanbul) edges of the European continent. Hagia Sophia, the former Greek Orthodox basilica, then a mosque, is now a museum in Istanbul.