Hagia Sophia (Turkish: Ayasofya, from the Greek: Ἁγία Σοφία, "Holy Wisdom"; Latin: Sancta Sophia or Sancta Sapientia) is a former Orthodox patriarchal basilica, later a mosque, now a museum in Istanbul, Turkey. Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture and to have "changed the history of architecture." It was the largest cathedral in the world for nearly a thousand years, until the completion of the Seville Cathedral in 1520. The current building was originally constructed as a church between 532 and 537 A.D. on the orders of the Byzantine Emperor Justinian, and was in fact the third Church of the Holy Wisdom to occupy the site. (The previous two had both been destroyed by riots.) It was designed by Isidore of Miletus, a physicist, and Anthemius of Tralles, a mathematician. The church contained a large collection of holy relics and featured, among other things, a 15 metre (49 foot) silver iconostasis. It was the seat of the Patriarch of Constantinople and the religious focal point of the Eastern Orthodox Church for nearly one thousand years. It was the church in which Cardinal Humbert in 1054 marched up to the altar and excommunicated Michael I Cerularius, which is commonly considered the start of the Great Schism.

Istanbul (Turkish: İstanbul, historically also known as Byzantium and Constantinople; see the names of Istanbul) is the largest city in Turkey and fifth largest city proper in the world with a population of 12.8 million. Istanbul is also a megacity, as well as the cultural and financial centre of Turkey. The city covers 39 districts of the Istanbul province. It is located on the Bosphorus Strait and encompasses the natural harbour known as the Golden Horn, in the northwest of the country. It extends both on the European (Thrace) and on the Asian (Anatolia) sides of the Bosphorus, and is thereby the only metropolis in the world that is situated on two continents.

In its long history, Istanbul has served as the capital city of the Roman Empire (330–395), the Eastern Roman (Byzantine) Empire (395–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). The city was chosen as joint European Capital of Culture for 2010. The historic areas of Istanbul were added to the UNESCO World Heritage List in 1985.

Turkey (Turkish: Türkiye), known officially as the Republic of Turkey ( Türkiye Cumhuriyeti ), is a Eurasian country that stretches across the Anatolian peninsula in Western Asia and Thrace in the Balkan region of southeastern Europe. Turkey is bordered by eight countries: Bulgaria to the northwest; Greece to the west; Georgia to the northeast; Armenia, Azerbaijan (the exclave of Nakhchivan) and Iran to the east; and Iraq and Syria to the southeast. The Mediterranean Sea and Cyprus are to the south; the Aegean Sea to the west; and the Black Sea is to the north.

Separating Anatolia and Thrace are the Sea of Marmara and the Turkish Straits (the Bosphorus and the Dardanelles), which are commonly reckoned to delineate the boundary between Europe and Asia, thereby making Turkey a country of significant geostrategic importance. Ethnic Turks form the majority of the population, followed by the Kurds. The predominant religion in Turkey is Islam and its official language is Turkish.