Sofia

Sofia has a humid continental climate (Köppen climate classification Dfb; Cfb if with −3 °C isotherm) with an average annual temperature of 10.9 °C (51.6 °F).

Winters are relatively cold and snowy. Weather can be very unstable and dynamic with sudden significant temperature amplitudes. In the coldest days temperatures can drop below −15 °C (5 °F), most notably in January. The lowest recorded temperature is −31.2 °C (−24 °F) (16 January 1893).[44][45] Fog is not unusual, especially in the beginning of the season. On average, Sofia receives a total snowfall of 96 cm (37.8 in) and 57 days with snow cover.[46] The snowiest recorded winter was 1995/1996 with a total snowfall of 171 cm (67.3 in).[47] The record snow depth is 57 cm (22.4 in) (25 December 2001).[48] The coldest recorded year was 1893 with an average January temperature of −10.4 °C (13 °F) and an annual temperature of 8.2 °C (46.8 °F).[49]

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 35 °C (95 °F) on the hottest days, particularly in July and August. The highest recorded temperature is 41 °C (106 °F) (5 July 2000 and 24 July 2007).[50][51]. Those values, however, were recorded at Sofia Airport, which is located at a slightly lower altitude compared to other parts of Sofia and lower than the average altitude of 550 m.[52] At that same time, the maximum temperatures recorded at the official weather station, located in Mladost district, were below 40 °C.[53][54] The hottest recorded month was July 2012 with an average temperature of 25 °C (77 °F).[55] The warmest year on record was 2019 with an annual temperature of 11.9 °C (53 °F).[56]

Springs and autumns in Sofia are usually short with variable and dynamic weather.

The city receives an average precipitation of 625.7 mm (24.63 in) 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 304.6 mm (11.99 in), while the wettest year on record was 2014 with a total precipitation of 1,066.6 mm (41.99 in).[57][58]

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.[75] 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.[76][77] As a result, air pollution levels in Sofia are some of the highest in Europe.[78]

Particulate matter concentrations are consistently above the norm.[77] During the October 2017 – March 2018 heating season, particulate levels exceeded the norm on 70 occasions;[76] on 7 January 2018, PM10 levels reached 632 µg/m³,[79] some twelve times the EU norm of 50 µg/m³.[80] Even areas with few sources of air pollution, like Gorna Banya, had PM2.5 and PM10 levels above safe thresholds.[79] 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.[81] 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.[82] Particulates are now largely measured by a network of 300 sensors maintained by volunteers since 2017.[76] The European Commission has taken Bulgaria to court over its failure to curb air pollution.[77]

The area has a history of nearly 7,000 years,[83] with the great attraction of the hot water springs that still flow abundantly in the centre of the city. The neolithic village in Slatina dating to the 5th–6th millennium BC is documented.[84] Remains from another neolithic settlement around the National Art Gallery are traced to the 3rd–4th millennium BC, which has been the traditional centre of the city ever since.[85]

The earliest tribes who settled were the Thracian Tilataei. In the 500s BC, the area became part of a Thracian state union, the Odrysian kingdom from another Thracian tribe the Odrysses.[86]

In 339 BC Philip II of Macedon destroyed and ravaged the town for the first time.[87]

The Celtic tribe Serdi gave their name to the city.[88] The earliest mention of the city comes from an Athenian inscription from the 1st century BC, attesting Astiu ton Serdon, i.e. city of the Serdi.[89] The inscription and Dio Cassius told that the Roman general Crassus subdued the Serdi and behanded the captives.[90]

In 27–29 BC, according do Dio Cassius, Pliny and Ptolemy, the region "Segetike" was attacked by Crassus, which is assumed to be Serdica, or the city of the Serdi.[91][92][93] The ancient city is located between TZUM, Sheraton Hotel and the Presidency.[85][94] It gradually became the most important Roman city of the region.[34][35] It became a municipium during the reign of Emperor Trajan (98–117). Serdica expanded, as turrets, protective walls, public baths, administrative and cult buildings, a civic basilica, an amphitheatre, a circus, the City council (Boulé), a large forum, a big circus (theatre), etc. were built. Serdica was a significant city on the Roman road Via Militaris, connecting Singidunum and Byzantium. In the 3rd century, it became the capital of Dacia Aureliana,[95] and when Emperor Diocletian divided the province of Dacia Aureliana into Dacia Ripensis (at the banks of the Danube) and Dacia Mediterranea, Serdica became the capital of the latter. Serdica's citizens of Thracian descent were referred to as Illyrians[87] probably because it was at some time the capital of Eastern Illyria (Second Illyria).[96]

Dated from the early 4th century, the Church of Saint George is the oldest standing edifice in Sofia.

When Emperor Diocletian divided the province of Dacia into Dacia Ripensis (on the banks of the Danube) and Dacia Mediterranea, Serdica became the capital of the latter.

Roman emperors Aurelian (215–275)[97] and Galerius (260–311)[98] were born in Serdica.

The city expanded and became a significant political and economical centre, more so as it became one of the first Roman cities where Christianity was recognised as an official religion (under Galerius). The Edict of Toleration by Galerius was issued in 311 in Serdica by the Roman emperor Galerius, officially ending the Diocletianic persecution of Christianity. The Edict implicitly granted Christianity the status of "religio licita", a worship recognised and accepted by the Roman Empire. It was the first edict legalising Christianity, preceding the Edict of Milan by two years.

Serdica was the capital of the Diocese of Dacia (337-602).

For Constantine the Great it was 'Sardica mea Roma est' (Serdica is my Rome). He considered making Serdica the capital of the Byzantine Empire instead of Constantinople.[99] which was already not dissimilar to a tetrarchic capital of the Roman Empire.[100] In 343 AD, the Council of Sardica was held in the city, in a church located where the current 6th century Church of Saint Sophia was later built.

The city was destroyed in the 447 invasion of the Huns and laid in ruins for a century[87] It was rebuilt by Byzantine Emperor Justinian I. During the reign of Justinian it flourished, being surrounded with great fortress walls whose remnants can still be seen today.

The 13th century lord of Sredets Kaloyan and his wife Desislava, Boyana Church

Serdica became part of the First Bulgarian Empire during the reign of Khan Krum in 809, after a long siege. The fall of the strategic city prompted a major and ultimately disastrous invasion of Bulgaria by the Byzantine emperor Nikephoros I, which led to his demise at the hands of the Bulgarian army.[101] In the aftermath of the war, the city was permanently integrated in Bulgaria and became known by the Slavic name of Sredets. It grew into an important fortress and administrative centre under Krum's successor Khan Omurtag, who made it a centre of Sredets province (Sredetski komitat, Средецки комитат). The Bulgarian patron saint John of Rila was buried in Sredets by orders of Emperor Peter I in the mid 10th century.[102] After the conquest of the Bulgarian capital Preslav by Sviatoslav I of Kyiv and John I Tzimiskes' armies in 970–971, the Bulgarian Patriarch Damyan chose Sredets for his seat in the next year and the capital of Bulgaria was temporarily moved there.[103] In the second half of 10th century the city was ruled by Komit Nikola and his sons, known as the "Komitopuli". One of them was Samuil, who was eventually crowned Emperor of Bulgaria in 997. In 986, the Byzantine Emperor Basil II laid siege to Sredets but after 20 days of fruitless assaults the garrison broke out and forced the Byzantines to abandon the campaign. On his way to Constantinople, Basil II was ambushed and soundly defeated by the Bulgarians in the battle of the Gates of Trajan.[102][104]

The city eventually fell to the Byzantine Empire in 1018, following the Byzantine conquest of Bulgaria. Sredets joined the uprising of Peter Delyan in 1040–1041 in a failed attempt to restore Bulgarian independence and was the last stronghold of the rebels, led by the local commander Botko.[105] During the 11th century many Pechenegs were settled down in Sofia region as Byzantine federats.

It was once again incorporated into the restored Bulgarian Empire in 1194 at the time of Emperor Ivan Asen I and became a major administrative and cultural centre.[106] Several of the city's governors were members of the Bulgarian imperial family and held the title of sebastokrator, the second highest at the time, after the tsar. Some known holders of the title were Kaloyan, Peter and their relative Aleksandar Asen (d. after 1232), a son of Ivan Asen I of Bulgaria (r. 1189–1196). In the 13th and 14th centuries Sredets was an important spiritual and literary hub with a cluster of 14 monasteries in its vicinity, that were eventually destroyed by the Ottomans. The city produced multicolored sgraffito ceramics, jewelry and ironware.[107]

In 1382/1383 or 1385, Sredets was seized by the Ottoman Empire in the course of the Bulgarian-Ottoman Wars by Lala Şahin Pasha, following a three-month siege.[108] The Ottoman commander left the following description of the city garrison: "Inside the fortress [Sofia] there is a large and elite army, its soldiers are heavily built, moustached and look war-hardened, but are used to consume wine and rakia—in a word, jolly fellows."[109]

From the 14th century till the 19th century Sofia was an important administrative center in the Ottoman Empire. It became the capital of the beylerbeylik of Rumelia (Rumelia Eyalet), the province that administered the Ottoman lands in Europe (the Balkans), one of the two together with the beylerbeylik of Anatolia. It was the capital of the important Sanjak of Sofia as well, including the whole of Thrace with Plovdiv and Edirne, and part of Macedonia with Thessaloniki and Skopje. [110]

During the initial stages of the Crusade of Varna in 1443, it was occupied by Hungarian forces for a short time in 1443, and the Bulgarian population celebrated a mass Saint Sofia Church. Following the defeat of the crusader forces in 1444, the city's Christians faced persecution. In 1530 Sofia became the capital of the Ottoman province (beylerbeylik) of Rumelia for about three centuries. During that time Sofia was the largest import-export-base in modern-day Bulgaria for the caravan trade with the Republic of Ragusa. In the 15th and 16th century, Sofia was expanded by Ottoman building activity. Public investments in infrastructure, education and local economy brought greater diversity to the city. Amongst others, the population consisted of Muslims, Bulgarian and Greek speaking Orthodox Christians, Armenians, Georgians, Catholic Ragusans, Jews (Romaniote, Ashkenazi and Sephardi), and Romani people.[108] The 16th century was marked by a wave of persecutions against the Bulgarian Christians, a total of nine became New Martyrs in Sofia and were sainted by the Orthodox Church, including George the New (1515), Sophronius of Sofia (1515), George the Newest (1530), Nicholas of Sofia (1555) and Terapontius of Sofia (1555).[111]

Sofia in mid-19th-century

When it comes to the cityscape, 16th century sources mention eight Friday mosques, three public libraries, numerous schools, 12 churches, three synagogues, and the largest bedesten (market) of the Balkans.[108] Additionally, there were fountains and hammams (bathhouses). Most prominent churches such as Saint Sofia and Saint George were converted into mosques, and a number of new ones were constructed, including Banya Bashi Mosque built by the renowned Ottoman architect Mimar Sinan. In total there were 11 big and over 100 small mosques by the 17th century.[112][113] In 1610 the Vatican established the See of Sofia for Catholics of Rumelia, which existed until 1715 when most Catholics had emigrated.[114] There was an important uprising against Ottoman rule in Sofia, Samokov and Western Bulgaria in 1737.

Sofia entered a period of economic and political decline in the 17th century, accelerated during the period of anarchy in the Ottoman Balkans of the late 18th and early 19th century, when local Ottoman warlords ravaged the countryside. 1831 Ottoman population statistics show that 42% of the Christians were non-taxpayers in the kaza of Sofia and the amount of middle-class and poor Christians were equal.[115] Since the 18th century the beylerbeys of Rumelia often stayed in Bitola, which became the official capital of the province in 1826. Sofia remained the seat of a sanjak (district). By the 19th century the Bulgarian population had two schools and seven churches, contributing to the Bulgarian National Revival. In 1858 Nedelya Petkova created the first Bulgarian school for women in the city. In 1867 was inaugurated the first chitalishte in Sofia – a Bulgarian cultural institution. In 1870 the Bulgarian revolutionary Vasil Levski established a revolutionary committee in the city and in the neighbouring villages. Following his capture in 1873, Vasil Levski was transferred and hanged in Sofia by the Ottomans.

During the Russo-Turkish War of 1877–78, Suleiman Pasha threatened to burn the city in defence, but the foreign diplomats Leandre Legay, Vito Positano, Rabbi Gabriel Almosnino and Josef Valdhart refused to leave the city thus saving it. Many Bulgarian residents of Sofia armed themselves and sided with the Russian forces.[116] Sofia was relieved (see Battle of Sofia) from Ottoman rule by Russian forces under Gen. Iosif Gurko on 4 January 1878. 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.[117]

Most mosques in Sofia were destroyed in that war, seven of them destroyed in one night in December 1878 when a thunderstorm masked the noise of the explosions arranged by Russian military engineers.[118][119] Following the war, the great majority of the Muslim population left Sofia.[108]

The allied bombing of Sofia in World War II in 1944

For a few decades after the liberation, Sofia experienced large population growth, mainly by migration from other regions of the Principality (Kingdom since 1908) of Bulgaria, and from the still Ottoman Macedonia and Thrace.

In 1900, the first electric lightbulb in the city was turned on.[120]

In the Second Balkan War, Bulgaria was fighting alone practically all of its neighbouring countries. When the Romanian Army entered Vrazhdebna in 1913, then a village 11 kilometres (7 miles) from Sofia, now a suburb,[121] this prompted the Tsardom of Bulgaria to capitulate. During the war, Sofia was flown by the Romanian Air Corps, which engaged on photoreconnaissance operations and threw propaganda pamphlets to the city. Thus, Sofia became the first capital on the world to be overflown by enemy aircraft.[122]

In 1925, a terrorist act of ultra-leftists failed their attempted assassination of the king but resulted in the destruction of the Saint Nedelya Church and many victims.

During the Second World War, Bulgaria declared war on the US and UK on 13 December 1941 and in late 1943 and early 1944 the US and UK Air forces conducted bombings over Sofia. As a consequence of the bombings thousands of buildings were destroyed or damaged including the Capital Library and thousands of books. In 1944 Sofia and the rest of Bulgaria was occupied by the Soviet Red Army and within days of the Soviet invasion Bulgaria declared war on Nazi Germany.

In 1945, the communist Fatherland Front took power. The transformations of Bulgaria into the People's Republic of Bulgaria in 1946 and into the Republic of Bulgaria in 1990 marked significant changes in the city's appearance. The population of Sofia expanded rapidly due to migration from rural regions. New residential areas were built in the outskirts of the city, like Druzhba, Mladost and Lyulin.

During the Communist Party rule, a number of the city's most emblematic streets and squares were renamed for ideological reasons, with the original names restored after 1989.[123]

The Georgi Dimitrov Mausoleum, where Dimitrov's body had been preserved in a similar way to the Lenin mausoleum, was demolished in 1999.

Borisova gradina

The city has an extensive green belt. Some of the neighbourhoods constructed after 2000 are densely built up and lack green spaces. There are four principal parks – Borisova gradina in the city centre and the Southern, Western and Northern parks. Several smaller parks, among which the Vazrazhdane Park, Zaimov Park, City Garden and the Doctors' Garden, are located in central Sofia. The Vitosha Nature Park (the oldest national park in the Balkans)[126] includes most of Vitosha mountain and covers an area of 266 square kilometres (103 sq mi),[127] with roughly half of it lying within the municipality of Sofia. Vitosha mountain is a popular hiking destination due to its proximity and ease of access via car and public transport. Two functioning cable cars provide year long access from the outskirts of the city. The mountain offers favourable skiing conditions during the winter. During the 1970s and the 1980s multiple ski slopes of varying difficulty were made available. Skiing equipment can be rented and skiing lessons are available. However, due to the bad communication between the private offshore company that runs the resort and Sofia municipality, most of the ski areas have been left to decay in the last 10 years, so that only one chairlift and one slope work.

A map of the 24 districts of Sofia

Sofia Municipality is identical to Sofia City Province, which is distinct from Sofia Province, which surrounds but does not include the capital itself. Besides the city proper, the 24 districts of Sofia Municipality encompass three other towns and 34 villages.[130] Districts and settlements have their own governor who is elected in a popular election. The assembly members are chosen every four years. The common head of Sofia Municipality and all the 38 settlements is the mayor of Sofia.[130] The mayor Yordanka Fandakova is serving a third consecutive term, having won the 2015 election at first round with 238,500 votes,[131] or 60.2% of the vote, when Reformist Bloc opponent Vili Lilkov was second with 9.6%; the turnout was 41.25%.[132] Some party leaders claimed that ballots were falsified and called for annulment of the election.[133] A precedent happened, due to the suspicion, as a preventative action between 300 and 5000 people and counters had been locked inside Arena Sofia (called Arena Armeets at the time) against their will for two days,[134] following which the director of the Electoral Commission of Sofia resigned at the request of Prime Minister Boyko Borisov.[135]

Sofia is the seat of the executive (Council of Ministers), legislative (National Assembly) and judiciary (Supreme Court and Constitutional Court) bodies of Bulgaria, as well as all government agencies, ministries, the National Bank, and the delegation of the European Commission. The President, along with the Council of Ministers, is located on Independence Square, also known as The Largo or The Triangle of Power.[138] One of the three buildings in the architectural ensemble, the former Bulgarian Communist Party headquarters, is due to become the seat of the Parliament. A refurbishment project is due to be completed in mid-2019,[139] while the old National Assembly building will become a museum or will only host ceremonial political events.[140]

The National Assembly building

The Council of Ministers (left), Presidency (right) and the former Communist Party House

Under Bulgaria's centralised political system, Sofia concentrates much of the political and financial resources of the country. It is the only city in Bulgaria to host three electoral constituencies: the 23rd, 24th and 25th Multi-member Constituencies, which together field 42 mandates in the 240-member National Assembly.[141]

With a murder rate of 1.7/per 100.000 people (as of 2009) Sofia is a quite safe capital city.[142] Nevertheless, in the 21st century, crimes, including Bulgarian mafia killings, caused problems in the city,[143] where authorities had difficulties convicting the actors,[144] which had caused the European Commission to warn the Bulgarian government that the country would not be able to join the EU unless it curbed crime[145] (Bulgaria eventually joined in 2007).[146] Many of the most severe crimes are contract killings that are connected to organised crime, but these had dropped in recent years after several arrests of gang members.[147] Corruption in Bulgaria also affects Sofia's authorities. According to the director of Sofia District Police Directorate, the largest share of the crimes are thefts, making up 62.4% of all crimes in the capital city. Increasing are frauds, drug-related crimes, petty theft and vandalism.[148] According to a survey, almost a third of Sofia's residents say that they never feel safe in the Bulgarian capital, while 20% always feel safe.[149] As of 2015, the consumer-reported perceived crime risk on the Numbeo database was "high" for theft and vandalism and "low" for violent crimes; safety while walking during daylight was rated "very high", and "moderate" during the night.[150] With 1,600 prisoners, the incarceration rate is above 0.1%;[151] however, roughly 70% of all prisoners are part of the Romani minority.[152]

Ivan Vazov National Theatre

Sofia concentrates the majority of Bulgaria's leading performing arts troupes. Theatre is by far the most popular form of performing art, and theatrical venues are among the most visited, second only to cinemas. There were 3,162 theatric performances with 570,568 people attending in 2014.[153] The Ivan Vazov National Theatre, which performs mainly classical plays and is situated in the very centre of the city, is the most prominent theatre. The National Opera and Ballet of Bulgaria is a combined opera and ballet collective established in 1891. Regular performances began in 1909. Some of Bulgaria's most famous operatic singers, such as Nicolai Ghiaurov and Ghena Dimitrova, made their first appearances on the stage of the National Opera and Ballet.

Cinema is the most popular form of entertainment: there were more than 141,000 film shows with a total attendance exceeding 2,700,000 in 2014.[154] Over the past two decades, numerous independent cinemas have closed and most shows are in shopping centre multiplexes. Odeon (not part of the Odeon Cinemas chain) shows exclusively European and independent American films, as well as 20th century classics. The Boyana Film studios was at the centre of a once-thriving domestic film industry, which declined significantly after 1990. Nu Image acquired the studios to upgrade them into Nu Boyana Film Studios, used to shoot scenes for a number of action movies like The Expendables 2, Rambo: Last Blood and London Has Fallen.[155][156]

The Museum of Contemporary Art

Bulgaria's largest art museums are located in the central areas of the city. Since 2015, the National Art Gallery, the National Gallery for Foreign Art (NGFA) and the Museum of Contemporary Art – Sofia Arsenal were merged to form the National Gallery. Its largest branch is Kvadrat 500, located on the NFGA premises, where some 2,000 works are on display in twenty eight exhibition halls.[157] The collections encompass diverse cultural items, from Ashanti Empire sculptures and Buddhist art to Dutch Golden Age painting, works by Albrecht Dürer, Jean-Baptiste Greuze and Auguste Rodin. The crypt of the Alexander Nevsky cathedral is another branch of the National Gallery. It holds a collection of Eastern Orthodox icons from the 9th to the 19th century.

The National History Museum, located in Boyana, it has a vast collection of more than 650,000 historical items dating from Prehistory to the modern era, although only 10,000 of them are permanently displayed due to the lack of space.[158] Smaller collections of historical items are displayed in the National Archaeological Museum, a former mosque located between the edifices of the National Bank and the Presidency. Two natural sciences museums—the Natural History Museum and Earth and Man—display minerals, animal species (alive and taxidermic) and rare materials. The Ethnographic Museum and the Museum of Military History hold large collections of Bulgarian folk costumes and armaments, respectively. The Polytechnical Museum has more than 1,000 technological items on display. The SS. Cyril and Methodius National Library, the foremost information repository in the country, holds some 1,800,000 books and more than 7,000,000 documents, manuscripts, maps and other items.[159]

Interior of the medieval Boyana Church

The Banya Bashi Mosque, an example of Ottoman architecture

The city houses many cultural institutes such as the Russian Cultural Institute, the Polish Cultural Institute, the Hungarian Institute, the Czech and the Slovak Cultural Institutes, the Italian Cultural Institute, Confucius Institute, Institut Français, Goethe Institut, British Council and Instituto Cervantes which regularly organise temporary expositions of visual, sound and literary works by artists from their respective countries.

Some of the biggest telecommunications companies, TV and radio stations, newspapers, magazines, and web portals are based in Sofia, including the Bulgarian National Television, bTV and Nova TV. Top-circulation newspapers include 24 Chasa and Trud.

The Boyana Church, a UNESCO World Heritage site, contains realistic frescoes, depicting more than 240 human images and a total 89 scenes, were painted. With their vital, humanistic realism they are a Renaissance phenomenon at its culmination phase in the context of the common-European art.[160]

Vitosha Boulevard, the main shopping street in the city

Cathedral dedicated to Aleksander Nevski

Sofia is one of the most visited tourist destinations in Bulgaria alongside coastal and mountain resorts. Among its highlights is the Alexander Nevsky Cathedral, one of the symbols of Bulgaria, constructed in the late 19th century. It occupies an area of 3,170 square metres (34,122 square feet) and can hold 10,000 people.

The city center contains many remains of ancient Serdica that have been excavated and are on public display, including Complex Ancient Serdica, eastern gate, western gate, city walls, thermal baths, 4th c. church of St. George Rotunda, amphitheatre of Serdica, the tombs and basilicas under the basilica of St. Sophia.

Vitosha Boulevard, also called Vitoshka, is a pedestrian zone with numerous cafés, restaurants, fashion boutiques, and luxury goods stores. Sofia's geographic location, in the foothills of the weekend retreat Vitosha mountain, further adds to the city's specific atmosphere.

Sofia is twinned with:

In addition Sofia cooperates with:

• Bulgarian News Agency (1898)
• Bulgarian National Radio (1935)
• Bulgarian National Television (1959)

• Nova Broadcasting Group (1994)
• bTV Media Group (2000)

• "Sofia in Figures" (PDF) (in Bulgarian and English). National Statistical Institute of Bulgaria. 2016. Retrieved 26 October 2018.
• Bozhilov, Ivan; Gyuzelev, Vasil (1999). История на средновековна България VII–XIV век [History of Medieval Bulgaria VII–XIV centuries] (in Bulgarian). Sofia: Анубис. ISBN 954-426-204-0.
• Stancheva, Magdalina (2010). София – от древността до нови времена [Sofia – from Antiquity to Modern Times] (in Bulgarian). Sofia: New Bulgarian University. ISBN 978-954-535-579-0.