Sofia ( SOH-fee-ə, SOF-, soh-FEE-ə; Bulgarian: Со́фия, translit. Sofiya, IPA: [ˈsɔfijə] (listen)) is the capital and largest city of Bulgaria. The city is at the foot of Vitosha Mountain in the western part of the country. Being in the centre of the Balkan peninsula, it is midway between the Black Sea and the Adriatic Sea, and closest to the Aegean Sea.Sofia has been an area of human habitation since at least 7000 BC. The recorded history of Sofia begins with the attestation of the conquest of Serdica by the Roman Republic in 29 BC from the Celtic tribe Serdi, raided by Huns in 343-347 AD and 447 AD, conquered by Visigoths in 376-382 AD, conquered by Avars and Slavs in 617 AD, and on 9th April, 809 Serdica was surrendered to Krum of Bulgaria. Bulgarian rule lasted until 1018, in 1040 and 1193-1382, which was interrupted by more than a century of Byzantine rule and by nearly five centuries-long Ottoman rule until Bulgarian rule was restored in 1878. During World War II Sofia was bombarded by the UK and US Air Forces and at the end of the war, it was seized by the Soviet Army. Being Bulgaria's primate city, Sofia is a hometown of many of the major local universities, cultural institutions and commercial companies. Sofia is one of the top 10 best places for start-up business in the world, especially in information technologies. Sofia was Europe's most affordable capital to visit in 2013.The population of Sofia declined down from 70,000 in the late 18th century, through 19,000 in 1870, to 11,649 in 1878 and began increasing. Sofia hosts some 1.23 million residents within a territory of 492 km2, a concentration of 17.5% of the country population within the 200th percentile of the country territory. The urban area of Sofia hosts some 1.54 million residents within 5723 km², which comprises Sofia City Province and parts of Sofia Province (Dragoman, Slivnitsa, Kostinbrod, Bozhurishte, Svoge, Elin Pelin, Gorna Malina, Ihtiman, Kostenets) and Pernik Province (Pernik, Radomir), representing 5.16% of the country territory. The metropolitan area of Sofia is based upon one hour of car travel time, stretches internationally and includes Dimitrovgrad in Serbia. Unlike most European metropolitan areas, it is not to be defined as a substantially functional metropolitan area, but is of the type with "limited variety of functions". The metropolitan region of Sofia is inhabited by a population of 1.68 million and is made up of the whole provinces Sofia City, Sofia and Pernik, comprising more than 10,000 km².