Sofia,(Bulgarian:), Bulgaria, the nation's capital and largest city. It lies in the upper Iskur River valley in western Bulgaria, just south of the Balkan Mountains. Sofia is the nation's leading commercial, industrial, and transportation center. It is also Bulgaria's main cultural and educational center.
Although most of Sofia has been built during the 20th century, the city has a few notable historic structures. Among these are the churches of St. George (4th-century Roman) and St. Sofia (6th-century Byzantine) and the Banya Bashi Mosque (16th-century Turkish). Alexander Nevski Cathedral (20th century) was built in memory of the Russian troops killed in the liberation of Bulgaria from the Turks (1876–78).
Major institutions include the National Library, the National Academy of Sciences, the National Opera, and the national museums of art, history, and archeology. The University of Sofia is Bulgaria's main institution of higher learning.
Sofia was a Thracian settlement when it was occupied by the Romans late in the first century A.D. It was soon raised to city status by Emperor Trajan. The city was destroyed by the Huns in the fifth century but was rebuilt by the Byzantines. Sofia was part of the first Bulgarian kingdom from 808 until 1018, when it reverted to Byzantine rule. The Bulgarians regained control in 1186. The city was conquered by the Ottoman Turks in the 1380's and for nearly 500 years was an administrative center for their Balkan possessions. When Bulgaria was made a principality in 1878, Sofia became its capital. The city has grown greatly since World War II.