Its ancient name Serdica derives from the local Celtic tribe of the Serdi who established the town in the 5th century BC. It remained a relatively small settlement until 1879, when it was declared the capital of Bulgaria.

The name Serdica or Sardica was popular in Latin, Ancient Greek and Byzantine Greek sources from Antiquity and the Middle Ages; it was related to the local Celtic tribe of the Serdi. The name was last used in the 19th century in a Bulgarian text, Service and hagiography of Saint George the New of Sofia: ВЪ САРДАКІИ.

Another of Sofia’s names, Triaditsa , was mentioned in Greek medieval sources. The Bulgarian name Sredets (СРѢДЄЦЪ), which is related to среда sreda (middle), first appeared in the 11th-century Vision of Daniel and was widely used in the Middle Ages.

The current name Sofia was first used in the 14th-century Vitosha Charter of Bulgarian tsar Ivan Shishman or in a Ragusan merchant’s notes of 1376; it refers to the famous Holy Sophia Church (Αγία Σοφία), an ancient church in the city named after the Christian concept of the Holy Wisdom. Although Sredets remained in use until the late 18th century, Sofia gradually overcame the Slavic name in popularity. During the Ottoman rule it was called Sofya by the Turkish conquerors of Bulgaria.

SOFIA is one of world’s richest capitals in mineral water. The city was found and developed based on its healing mineral and thermal springs, and has appeared in written records since 2,400 years back. The city of Sofia (Ulpia Serdica) experienced intensive growth during the Roman presence in the 2nd century AD, when it became a center for political and cultural life. Emperor Constantine the Great used to call Serdica “My Rome,” and considered making it the capital of the Eastern Roman Empire.