Antiquity
Sofia was originally a Thracian settlement called Serdica, or Sardica, possibly named after the Celtic tribe Serdi. For a short period during the 4th century BC, the city was ruled by Philip of Macedon and his son Alexander the Great. Around BC 29, Serdica was conquered by the Romans. It became a municipium, or centre of an administrative region, during the reign of Emperor Trajan (98�117) and was renamed Ulpia Serdica. It seems that the first written mention of Serdica was made by Ptolemy (around 100 AD). Serdica (Sardica) expanded, as turrets, protective walls, public baths, administrative and cult buildings, a civic basilica, an amphitheatre � the City Council (Boul�), a large Forum, a big Circus (Theatre), etc. were built.
When Emperor Diocletian divided the province of Dacia into Dacia Ripensis (at the banks of the Danube) and Dacia Mediterranea, Serdica became the capital of Dacia Mediterranea. The city subsequently expanded for a century and a half, it became a significant political and economical centre, moreso � it became one of the first Roman cities where Christianity was recognized as an official religion (?mperor Galerius). In 343 AD, the Council of Sardica was held in the city, in a church located where the current 6th century Church of Saint Sophia was later built.
The city was destroyed in the 447 invasion of the Huns. It was rebuilt by Byzantine Emperor Justinian I and for a while called Triaditsa or Sredets by the slavonic tribes. During the reign of Justinian it flourished, being surrounded with great fortress walls whose remnants can still be seen today.
Middle Ages and Ottoman rule
Sofia first became part of the First Bulgarian Empire during the reign of Khan Krum in 809, after a long siege. Afterwards, it was known by the Bulgarian name "Sredets" and grew into an important fortress and administrative centre. After the fall of North-eastern Bulgaria under John I Tzimiskes' armies in
