Migrating Slavs began to filter into the city in the seventh century, becoming the dominant force in the region after Serdica's capture by the Bulgar Khan Krum in 809. The city continued to flourish under the Bulgarians, although few medieval cultural monuments remain, save for the thirteenth-century Boyana church . Re-named Sredets by the Slavs (and subsequently Triaditsa by the Byzantines), the city became known as Sofia sometime in the fourteenth century, most probably taking its name from the ancient Church of Sveta Sofia (Holy Wisdom) which still stands in the city centre. Five centuries of Ottoman rule began with the city's capture in 1382, during which time Sofia thrived as a market centre, though little material evidence of the Ottoman period remains save for a couple of mosques .

Economic decline set in during the nineteenth century, hastened by earthquakes in 1852. Sofia was a minor provincial centre at the time of the Liberation in 1878, when defeat of the Ottoman Empire by Russian forces paved the way for the foundation of an independent Bulgarian state. Sofia was chosen to become the new capital of the country in preference to more prestigious centres (such as TA?rnovo in central Bulgaria) because of its geographical location: situated on a wide plain fringed by mountains, Sofia combined defensibility with the potential for future growth. It was also thought that it would occupy a central position in any Bulgarian state which included (as was then hoped) Macedonia. The Bulgarians were keen to stamp their identity on the city right at the outset. Mosques were demolished or turned to other uses, and 6000 of the city's Turks chose to emigrate. Sofia underwent rapid development after 1878, although progress sometimes sat uneasily beside backwardness and poverty. The Czech historian and educationalist Konstantin Jirecaek - one of many foreign experts brought in to help run the new state - dubbed Sofia boklukopolis ("trashville") in recognition of its chaotic post-Liberation appearance. However foreign observers were on the whole impressed by the way in which the Bulgarians speedily improvised a capital city out of nothing. "I had expected a semi-barbaric Eastern town," remarked Frank Cox, the Morning Post 's Balkan correspondent in 1913, "but I found a modern capital, small but orderly, clean and well-manageda?¦but oh, so deadly dull." Despite its increasing prosperity, Sofia didn't experience much of a belle A©poque, save for the lavish palace balls presided over by the mercurial Tsar Ferdinand, and the weekly dances at the military club.

The city experienced more frenetic growth during the post-World War II era of "socialist construction", and a veneer of Stalinist monumentalism was added to the city centre in the shape of buildings like the Party House , a stern-looking expression of political authority. Sofia's rising population was housed in the endless high-rise suburbs (places with declamatory names like Mladost - "Youth", Druzhba - "Friendship", and Nadezhda - "Hope") that girdle the city today.

The factories that used to employ the inhabitants of these suburbs went into a steep decline during the 1980s and collapsed totally in the 1990s, leading to high unemployment and a drop in living standards. However Sofia has coped with the transition from communism to capitalism better than most Bulgarian towns. New businesses are springing up all the time (though many go bust just as quickly), jobs are easier to come by here than elsewhere, and the population has been swelled by migrants from provincial towns blighted by economic stagnation. Sofia's city council has made small but significant steps in turning the capital into a modern European metropolis, re-paving central sidewalks and providing key central buildings with a much-needed facelift. Even so, much about contemporary Sofia remains strange or surprising: walking through the quiet, under-lit streets at night often makes you feel as if you're in a small provincial town rather than a million-strong urban sprawl. No less unsettling to the first-time visitor is the visible presence of a large stray dog population in Sofia's downtown streets. Officially there are 35,000 of the beasts roaming the city, but the real figure may be up to three times higher. Although pretty docile during the day, the dog packs become territorial at night, when lone pedestrians can become the victims of massed barking, or worse. Potentially more dangerous, however, are the four-legged brutes acquired by suburban Sofians to act as guard dogs or status symbols.