The capital and largest city of Bulgaria, in the west-central part of the country. Originally a Thracian settlement, it passed over the centuries to Rome, Byzantium, two Bulgarian kingdoms, Ottoman Turkey, and Russia. In 1879 it became the capital of independent Bulgaria. During World War II the city was occupied by German forces. It was liberated (1944) by the Soviets, who installed a Communist government. Sofia is the leading commercial, industrial, and transportation center of Bulgaria.