Georgia ( ( listen); Georgian: საქართველო, translit.: sakartvelo, IPA: [sɑkʰɑrtʰvɛlɔ] ( listen)) is a country in the Caucasus region of Eurasia. Located at the crossroads of Western Asia and Eastern Europe, it is bounded to the west by the Black Sea, to the north by Russia, to the south by Turkey and Armenia, and to the southeast by Azerbaijan. The capital and largest city is Tbilisi. Georgia covers a territory of 69,700 square kilometres (26,911 sq mi), and its 2017 population is about 3.718 million. Georgia is a unitary semi-presidential republic, with the government elected through a representative democracy. During the classical era, several independent kingdoms became established in what is now Georgia, such as Colchis, later known as Lazica and Iberia. The Georgians adopted Christianity in the early 4th century. The common belief had an enormous importantce for spiritual and political unification of early Georgian states. A unified Kingdom of Georgia reached its Golden Age during the reign of King David IV and Queen Tamar in the 12th and early 13th centuries. Thereafter, the kingdom declined and eventually disintegrated under hegemony of various regional powers, including the Mongols, the Ottoman Empire, and successive dynasties of Iran.