A Thracian settlement once occupied the site of Sofia. It was taken by the Romans in a.d. 29 and flourished, especially, under the Emperor Trajan, as Sardica. Destroyed by the Huns in 447, the city was rebuilt (6th cent.) by Byzantine emperor Justinian I and renamed Triaditsa by the Byzantines. It formed part of the first Bulgarian kingdom (809-1018), reverted to the Byzantines (1018-1186), and was included in the second Bulgarian kingdom (1186-1382). Known as Sredets under the Bulgars, it was renamed Sofia or Sophya in 1376. Sofia passed to the Ottomans in 1382 and became the residence of the Turkish governors of Rumelia. Taken by the Russians in the Russo-Turkish War of 1877-78, it became (1879) the capital of newly independent Bulgaria. During World War II the Russians captured Sofia from the Germans (1944).

The city has a university (founded 1889) and numerous other educational and cultural facilities. It is the see of an Eastern Orthodox metropolitan and of a Roman Catholic bishop and also retains many old churches, mosques, and synagogues. Landmarks include the parliament building, the state opera house, the former royal palace, the Church of St. George (4th-5th cent.), the Church of St. Sofia (6th-7th cent.), the Banya Bashi mosque (1474), and the Alexander Nevski Cathedral.