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 (Boulé), 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 (Еmperor Galerius). So it was only very natural that Constantine the Great called Serdica (Sardica) "My Rome".
In 343 AD, the Council of Sardica was held in the city, in a church located where the current 6th century Church of Saint Sofia was later built. Serdica was of moderate size, but magnificent as an urban concept of urban planning and architecture, with abundant amusements and an active social life.
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.
Sofia was taken by Russian forces on January 4, 1878, during the Russo-Turkish War, 1877-78, and became the capital of the autonomous Principality of Bulgaria in 1879, which became the Kingdom of Bulgaria in 1908. It was proposed as a capital by Marin Drinov and was accepted as such on 3 April 1879. By the time of its liberation the population of the city was 11,649. For a few decades after the liberation the city experienced large population growth mainly from other regions of the country.
During World War II, Sofia was bombed by Allied aircraft - British and USA aircraft, in late 1943 and early 1944. As a consequence of the invasion of the Soviet Red Army, Bulgaria's government, which was allied with Germany, was overthrown.
According to 2010 data, the whole Capital Municipality, with a population of 1,376,467 and had a population density of 926.5.
The ratio of women per 1,000 men was 1,102. The birth rate per 1000 people was 12.3 per mille and steadily increasing in the last 5 years, the death rate reaching 12.1 per mille and decreasing. The natural growth rate during 2009 was 0.2 per mille, the first positive growth rate in nearly 20 years. The considerable immigration to the capital from poorer regions of the country, as well as urbanisation, are among the other reasons for the increase in Sofia's population. 4.8 people of every one thousand were wedded in 2009 (only heterosexual marriage is possible in Bulgaria) and the infant mortality rate was 5.6 per 1,000, down from 18.9 in 1980.
According to the 2001 census, Sofia's population is made up of 96% ethnic Bulgarians; among minority communities, nearly 18,000 (1.5%) officially identified themselves as Roma, 6,000 as Turkish, 3,000 as Russian, 1,700 as Armenian, and 1,200 as Greek.
The unemployment is lower than in other parts of the country — 2.45% of the active population in 1999 and declining, compared to 7.25% for the whole of Bulgaria as of 1 July 2007. The large share of unemployed people with higher education, 27% as compared to 7% for the whole country, is a characteristic feature of the capital.
Sofia was declared capital in 1879. One year later, in 1880, it was the fifth-largest city in the country after Plovdiv, Varna, Ruse and Shumen. Plovdiv remained the most populous Bulgarian town until 1892 when Sofia took the lead.
With its developing infrastructure and strategic location, Sofia is an important centre for international railway and automobile routes. Three Trans-European Transport Corridors cross the city: 4, 8 and 10. All major types of transport (except water transport) are represented in the city. It is home to eight railway stations, the biggest of which is the Central Railway Station. Just next to it is the new Central Bus Station, the biggest and most modern of its kind in the country. A number of other Bus Stations allow interurban and international trips from different parts of the city. The Sofia Airport with its new second terminal, finished in 2006, handled some 2.7 million passengers in 2007.
Public transport is well-developed with bus, tram (153,6 km network) and trolleybus (97 km network) lines running in all areas of the city, although some vehicles are in a poor condition. The Sofia underground became operational from 1998 and is yet largely underdeveloped with one line and only 14 stations. Several new stations have been opened in 2009. Another, second line is being built with a targeted completion date in 2012. The masterplan for the Sofia underground includes three lines with a total of 47 stations. In recent years the marshrutka, a private passenger van, began serving fixed routes and proved an efficient and popular means of transport by being faster than public transport but cheaper than taxis. As of 2005 these vans numbered 368 and serviced 48 lines around the city and suburbs. There are some 6,000 licensed taxi cabs operating in the city and another 2,000 operating somewhat illegally. Low fares in comparison with other European countries, make taxis affordable and popular among a big part of the city population.
Private automobile ownership has grown rapidly in the 1990s; more than 1,000,000 cars were registered in Sofia in the last five years. The Sofia municipality is known for minor and cosmetic repairs and most streets are in a poor condition. Consequently traffic and air pollution problems have become more severe and receive regular criticism in local media. The extension of the underground system is hoped to alleviate the city's immense traffic problems.
Sofia has a unique, very large combined heat and power (CHP) plant. Virtually the entire city (900,000 households and 5,900 companies) is centrally heated, using residual heat from electricity generation (3,000 MW) and gas- and oil-fired heating furnaces; total heat capacity is 4,640 MW. The heat distribution piping network is 900 km long and comprises 14,000 substations and 10,000 heated buildings.
A number of ancient Roman, Byzantine and medieval Bulgarian buildings have been preserved in the city and its outskirts. Most notably, the 10th century Boyana Church (one of the UNESCO World Heritage protected sites), the Church of St. George, considered the oldest building in Sofia, and the early Byzantine Church of St Sophia.
A medieval monument of significant interest is the Church of St Petka of the Saddlers located in the very centre of the city providing a sharp contrast to the surrounding three Socialist Classicism edifices of the former Party House, TZUM, and Sheraton Sofia Hotel Balkan.
After the Liberation of Bulgaria from Ottoman rule in 1878 and the establishment of an autonomous Bulgarian monarchy with its capital in Sofia, Knyaz Alexander Battenberg invited architects from Austria-Hungary to shape the new capital's architectural appearance.
Among the architects invited to work in Bulgaria were Friedrich Grünanger, Adolf Václav Kolář, Viktor Rumpelmayer and others, who designed the most important public buildings needed by the newly-reestablished Bulgarian government, as well as numerous houses for the country's elite. Later, many foreign-educated Bulgarian architects also contributed.
The architecture of Sofia's centre is thus a combination of Neo-Baroque, Neo-Rococo, Neo-Renaissance and Neoclassicism, with the Vienna Secession also later playing an important part, but it is mostly typically Central European.
Among the most important buildings constructed in Sofia in the period are the former royal palace, today housing the National Art Gallery and the National Ethnographic Museum (1882); the Ivan Vazov National Theatre (1907); the former royal printing office, today the National Gallery for Foreign Art; the National Assembly of Bulgaria (1886), the Bulgarian Academy of Sciences (1893), etc.
After the Second World War and the establishment of a Communist government in Bulgaria in 1944, the architectural line was substantially altered. Socialist Classicism public buildings emerged in the centre, but as the city grew outwards, the new neighbourhoods were dominated by many concrete tower blocks, prefabricated panel apartment buildings (panelki) and examples of Brutalist architecture.
After the abolishment of Communism in 1989, Sofia has witnessed the construction of whole business districts and neighbourhoods, as well as modern skryscraper-like glass-fronted office buildings, but also top-class residential neighbourhoods. Capital Fort Business Center will be the first skyscraper in Bulgaria with its 126 m and 36 floors.
Furthermore, institutions of national significance, such as the Bulgarian Academy of Sciences and the SS. Cyril and Methodius National Library are located in Sofia. The American College of Sofia, founded in 1860 and often regarded as the oldest American academic institution outside the United States, provides secondary education to some of Bulgaria's brightest students.
The St. Clement of Ohrid University of Sofia is the oldest higher education institution in Bulgaria, founded on 1 October 1888. The university's edifice was constructed between 1924 and 1934 with the financial support of the brothers Evlogi Georgiev and Hristo Georgiev.
Most football stadiums have tennis courts, astroturf pitches and other sports facilities joined to them, and there are other such facilities scattered throughout the city, mainly in the parks.
There are also various other all-round sports complexes in the city which belong to institutions other than the football clubs, such as those of the National Sports Academy, of the Bulgarian Academy of Sciences, or those of the capital's various universities.
There are more than fifteen swimming complexes in the city, most of them outdoor. Nearly all of these were constructed as competition venues and therefore have seating facilities for several hundred people.
There are two golf courses just to the east of Sofia — in Elin Pelin (St Sofia club) and in Ihtiman (Air Sofia club), and a horseriding club (St George club).
The capital's main attraction is probably the ample opportunity provided to Sofianites for making use of the city's sprawling parklands, many of which are densely forested. There are four such major parks - Tsar Boris's Garden in the city centre, as well as the Southern, Western and Northern and several other smaller parks, most notable of which are the City Garden and the Doctor Garden. The Vitosha Nature Park (the oldest national park in the Balkans ), which includes a big part of the Vitosha mountain to the south of Sofia, covers an area of almost 270 km² and lies entirely within the city limits. Many Sofianites take weekly hikes up the mountain, and most do so at least a couple of times a year. There are bungalows as well as several ski slopes on Vitosha, allowing locals to take full advantage of the countryside and of the mountains without having to leave the city.
The Pancharevo lake area is a popular destination due to its scenery, historical heritage (Urvich fortress and Pancharevo monastery), as well as Bulgaria's largest rowing base - "Sredets".