Sofia () (Bulgarian: София, Sofiya,pronounced [ˈsɔfijɐ]) is the capital and largest city of Bulgaria. Sofia is the 15th largest city in the European Union with population of more than 1.2 million people. The city is located at the foot of Vitosha Mountain in the western part of the country, within less than 50 kilometres (31 mi) drive from the Serbian border. Its location in the centre of the Balkan peninsula means that it is the midway between the Black Sea and the Adriatic Sea, whereas the Aegean Sea is the closest to it.
Sofia has been an area of human habitation since at least 7000 BCE. Many of the major universities, cultural institutions and commercial companies of Bulgaria are concentrated in Sofia. Sofia is one of the top 10 best places for start-up business in the world, especially in IT technologies. Sofia is Europe's most affordable capital to visit as of 2013.
For the longest time the city possessed a Thracian name, derived from the tribe Serdi, who were either of Thracian,Celtic, or mixed Thracian-Celtic origin. The Serdi and the name of emperor Marcus Ulpius Traianus (53 – 117 AD) prompted the Romans to give the city the combinative name of Ulpia Serdica; Ulpia is derived from an Umbrian cognate of the Latin word lupus, meaning "wolf."
It seems that the first written mention of Serdica was made during his reign and the last mention was in the 19th century in a Bulgarian text (Сардакіи, Sardaki). During the Romans civitas Serdenisium was mentioned the "brightest city of the Serdi" in official inscriptions. The city was major throughout the past ever since Antiquity, when Roman emperor Constantine the Great referred to it as "my Rome", and it nearly became his capital.