Sofia

Sofia is the capital and largest city of Bulgaria. It is situated in the Sofia Valley at the foot of the Vitosha mountain, in the western part of the country. The city is built west of the Iskar river and has many mineral springs, such as the Sofia Central Mineral Baths. It has a humid continental climate.
Known as Serdica in antiquity, Sofia has been an area of human habitation since at least 7000 BC. The recorded history of the city begins with the attestation of the conquest of Serdica by the Roman Republic in 29 BC from the Celtic tribe Serdi. During the decline of the Roman Empire, the city was raided by Huns, Visigoths, Avars, and Slavs. In 809, Serdica was incorporated into the First Bulgarian Empire by Khan Krum and became known as Sredets. In 1018, the Byzantines ended Bulgarian rule until 1194, when it was reincorporated by the Second Bulgarian Empire. Sredets became a major administrative, economic, cultural and literary hub until its conquest by the Ottomans in 1382. From 1530 to 1836, Sofia was the regional capital of Rumelia Eyalet, the Ottoman Empire's largest and most important province. Bulgarian rule was restored in 1878. Sofia was selected as the capital of the Third Bulgarian State in the next year, ushering a period of intense demographic and economic growth.
Sofia is the 14th-largest city in the European Union. It is surrounded by mountains including Vitosha to the south, Lyulin to the west, and the Balkan Mountains to the north. It is the third highest European capital after Andorra la Vella and Madrid. Sofia is home to several universities, cultural institutions and commercial companies. The city has been described as the "triangle of religious tolerance". This is because three temples of three major world religions—Christianity, Islam and Judaism—are situated close together: Sveta Nedelya Church, Banya Bashi Mosque and Sofia Synagogue. This triangle was recently expanded to a "square" and includes the Catholic Cathedral of St Joseph.
The Boyana Church in Sofia, constructed during the Second Bulgarian Empire and holding much patrimonial symbolism to the Bulgarian Orthodox Church, was included onto the World Heritage List in 1979. With its cultural significance in Southeast Europe, Sofia is home to the National Opera and Ballet of Bulgaria, the National Palace of Culture, the Vasil Levski National Stadium, the Ivan Vazov National Theatre, the National Archaeological Museum, and the Serdica Amphitheatre. The Museum of Socialist Art includes many sculptures and posters that educate visitors about the lifestyle in communist Bulgaria.
The population of Sofia declined from 70,000 in the late 18th century, through 19,000 in 1870, to 11,649 in 1878, after which it began increasing. Sofia hosts some 1.28 million residents within a territory of 500 km², a concentration of 17.9% of the country's population within the 200th percentile of the country's territory. The urban area of Sofia hosts some 1.5 million residents within 5723 km², which comprises Sofia City Province and parts of Sofia Province and Pernik Province, 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. The metropolitan region of Sofia is inhabited by a population of 1.6 million.

Names

For a long time, the city possessed the name, Serdica, derived from the tribe Serdi, who were either of Thracian, Celtic, or mixed Thracian-Celtic origin. The emperor Marcus Ulpius Traianus gave the city the combinative name of Ulpia Serdica; Ulpia may be derived from an Umbrian cognate of the Latin word lupus, meaning "wolf" or from the Latin vulpes. 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. Other names given to Sofia, such as Serdonpolis and Triaditza, were mentioned by Byzantine Greek sources or coins. The Slavic name Sredets, which is related to "middle" and to the city's earliest name, first appeared on paper in an 11th-century text. The city was called Atralisa by the Arab traveller Idrisi and Strelisa, Stralitsa, or Stralitsion by the Crusaders.
The name Sofia comes from the Saint Sofia Church, as opposed to the prevailing Slavic origin of Bulgarian cities and towns. The origin is in the Greek word sophía. The earliest works where this latest name is registered are the duplicate of the Gospel of Serdica, in a dialogue between two salesmen from Dubrovnik around 1359, in the 14th-century Vitosha Charter of Bulgarian tsar Ivan Shishman and in a Ragusan merchant's notes of 1376. In these documents, the city is called Sofia, but, at the same time, the region and the city's inhabitants are still called Sredecheski, which continued until the 20th century. The Ottomans came to favour the name Sofya. In 1879, there was a dispute about what the name of the new Bulgarian capital should be, when the citizens created a committee of famous people, insisting for the Slavic name. Gradually, a compromise arose, officialisation of Sofia for the nationwide institutions, while legitimating the title Sredets for the administrative and church institutions, before the latter was abandoned through the years.

Geography

has an area of 1344 km², while the surrounding and much bigger Sofia Province is 7,059 km². Sofia's development as a significant settlement owes much to its central position in the Balkans. It is situated in western Bulgaria, at the northern foot of the Vitosha mountain, in the Sofia Valley that is surrounded by the Balkan mountains to the north. The valley has an average altitude of. Sofia is the second highest capital of the European Union and the third highest capital of Europe. Unlike most European capitals, Sofia does not straddle any large river, but is surrounded by comparatively high mountains on all sides. Three mountain passes lead to the city, which have been key roads since antiquity, Vitosha being the watershed between Black and Aegean Seas.
A number of shallow rivers cross the city, including the Boyanska, Vladayska and Perlovska. The Iskar River in its upper course flows near eastern Sofia. It takes its source in Rila, Bulgaria's highest mountain, and enters Sofia Valley near the village of German. The Iskar flows north toward the Balkan Mountains, passing between the eastern city suburbs, next to the main building and below the runways of Vasil Levski Sofia Airport, and flows out of the Sofia Valley at the town of Novi Iskar, where the scenic Iskar Gorge begins.
The city is known for its 49 mineral and thermal springs. Artificial and dam lakes were built in the twentieth century.
While the 1818 and 1858 earthquakes were intense and destructive, the 2012 Pernik earthquake occurred west of Sofia with a moment magnitude of 5.6 and a much lower Mercalli intensity of VI. The 2014 Aegean Sea earthquake was also noticed in the city.

Climate

Sofia has a humid continental climate with an average annual temperature of.
Winters are relatively cold and snowy. In the coldest days temperatures can drop below, most notably in January. The lowest recorded temperature is . On average, Sofia receives a total snowfall of and 56 days with snow cover. The snowiest recorded winter was 1939/1940 with a total snowfall of. The record snow depth is . The coldest recorded year was 1893 with an average January temperature of and an annual temperature of.
Summers are quite warm and sunny. In summer, the city generally remains slightly cooler than other parts of Bulgaria, due to its higher altitude. However, the city is also subject to heat waves with high temperatures reaching or exceeding on the hottest days, particularly in July and August. The highest recorded temperature is . The hottest recorded month was July 2012 with an average temperature of. The warmest year on record was 2024 with an annual temperature of.
Springs and autumns in Sofia are usually short with variable and dynamic weather.
The city receives an average precipitation of a year, reaching its peak in late spring and early summer when thunderstorms are common. The driest recorded year was 2000 with a total precipitation of, while the wettest year on record was 2014 with a total precipitation of.

Environment

The geographic position of the Sofia Valley limits the flow of air masses, increasing the chances of air pollution by particulate matter and nitrogen oxide. Solid fuel used for heating and motor vehicle traffic are significant sources of pollutants. Smog thus persists over the city as temperature inversions and the mountains surrounding the city prevent the circulation of air masses. As a result, air pollution levels in Sofia are some of the highest in Europe.
Particulate matter concentrations are consistently above the norm. During the October 2017 – March 2018 heating season, particulate levels exceeded the norm on 70 occasions; on 7 January 2018, PM10 levels reached 632 μg/m³, some twelve times the EU norm of 50 μg/m³. Even areas with few sources of air pollution, like Gorna Banya, had PM2.5 and PM10 levels above safe thresholds. In response to hazardous spikes in air pollution, the Municipal Council implemented a variety of measures in January 2018, like more frequent washing of streets. However, a report by the European Court of Auditors issued in September 2018 revealed that Sofia has not drafted any projects to reduce air pollution from heating. The report also noted that no industrial pollution monitoring stations operate in Sofia, even though industrial facilities are active in the city. A monitoring station on Eagles' Bridge, where some of the highest particulate matter values were measured, was moved away from the location and has measured sharply lower values since then. Particulates are now largely measured by a network of 300 sensors maintained by volunteers since 2017. The European Commission has taken Bulgaria to court over its failure to curb air pollution.