A white mammoth dominates the upper part of Boulevard Todor Aleksandrov in central Sofia. Its massive, concrete surfaces are imposing. Looking from the lower ground of the Serdica station, the building, Unicredit Bulbank's headquarters, resembles a giant ocean steamer which is about to crush the Largo, the vast space surrounded by the Stalinist Council of Ministers, the Office of the President and the former Communist Party House, now parliament.

The architectural style of Brutalism is having a global moment right now: social media users fervently discuss whether or not a particular building belongs to the style, there are plenty of photo books dedicated to it and scientists write articles about it. Brutalism is also in the movies, particularly the dystopian ones.

What is Brutalism? In 1952, Swiss architect and urbanist Le Corbusier defined "le béton brut." Brutalism, originally called New Brutalism, uses bare building materials, such as concrete, and clearly visible structural elements. The style was to symbolise the post-war welfare state and was a part of the modernist movement, sharing its principle of "form forever follows function."

The Communist-era Foreign Trade Bank building across the square from the Council of Ministers is of the finest examples of Brutalist architecture in Bulgaria. It now houses the commercial UniCredit Bulbank

The East bloc soon embraced Brutalism as it suited the Communist regimes both economically and ideologically. It provided a cheap and fast way to build the necessary housing stock. Its imposing buildings were ideal to impress the masses. At the time, the East bloc was building not only homes, but also Communism. Its "great" leaders called themselves "Builders of Socialism."

The planned economy applied its rules not only to the market, but also to urbanisation. In Bulgaria, the 1951 Ordinance on Planned Construction prescribed: "The projects and bills of accounts of all state construction sites as well as those of the cooperatives, the political and public organisations shall be made only by the respective designer organisations." All over the country, dedicated work teams like Glavproekt, Sofproekt and Touristproekt were planning developments.

As early as 1948, the People's Republic of Bulgaria planned to develop summer resorts all over the Black Sea coast. Georgi Ganev, chief architect at Glavproekt, designed the 1956 master plan for Golden Sands, and Nikola Nikolov, who was active in party politics, designed the 1957 master plan of Sunny Beach. The Black Sea coast became a showcase of Bulgarian architecture and a laboratory for Bulgarian architects.

Besides the resorts at the Black Sea and the hotels and bars at other tourist sites, the regime used the style for residential and office buildings, cultural venues, sports infrastructure and countless Party houses. The style's imposing nature suited well Communist monuments, most notably the Buzludzha Communist Party Memorial House, designed by Georgi Stoilov in 1974. Nicknamed Flying Saucer, it has an iconic status among Brutalist aficionados all over the world.

The term Brutalism evokes unappealing concrete monoliths. Yet "brut" stands for bare, not brute. In Sofia, the former House of Soviet Science and Culture (1974), today's Russian Centre, was one of Bulgaria's first buildings in raw concrete. Stripping each decorative element and simplifying the exterior to concrete surfaces around a glazed entrance, architects Georgi Berberov and Ivo Tsolov clearly strove for purity of style, and thus form.

Built in 1979 as a Balkanturist project and Sofia's tallest building at the time, hotel Rodina, or Motherland, is a quintessential Brutalist building. Designed by architect Todor Kozhuharov and his team, it is all about large-scale concrete and hardly any decoration. Supporting elements are not hidden, but accentuated. A pattern repeats itself all over the façade. The hotel now is called Astoria.

Glavproekt was the country's largest state institute of architecture and urban planning and employed over a thousand architects, engineers and technicians. A generation of young architects working with Glavproekt or Nikolov developed Bulgaria's local version of Brutalism.

In Bulgaria, few buildings are in pure Brutalist style. Compared with other nations, in particular neighbouring Serbia, whose Yugoslavian monoliths are in a league of their own, Bulgaria's Brutalism seems somewhat mitigated: it misses the larger-than-life aspect and its mixture of materials renders it less austere and more human. Even the National Palace of Culture (1981), designed by Alexander Barov, which was to be a showcase for the regime, looks more elegant than most of its fellow Communist counterparts.

A fine example of this approach is a five-storey apartment building for the regime's top brass on Sofia's Veliko Tarnovo Street, built in 1980. Architects Nikola Antonov and Bogdan Tomalevski used a repeating pattern in concrete to enclose the balconies and made the wooden window frames and ceilings prominent. At the time, Brutalism represented modernity, progress and comfort, and was popular among the nomenklatura.

Conforming to the National-by-Form-Socialist-by-Content motto, Bulgarian architects incorporated traditional Bulgarian elements into the rigid framework of the international style. In the headquarters of Unicredit Bulbank, for example, the cantilevered upper floor with its arched windows evoke a chardak, or wooden covered terrace, a typical element in 19th century traditional architecture in Bulgaria. Niches in the walls refer to the ancient church that used to exist in this spot.

Architects also used widely and wisely art by established artists. For example, Sofia's Universiada sports hall (1961), designed by Alexandar Barov, Ivan Tatarov, Doncho Vladishki and Ivan Ivanchev, has a mosaic by the famed painter-sculptor Lyubomir Dalchev.

Architects also fused Brutalism with other, foreign styles. The three imposing towers of the diplomatic corps buildings in Sofia's Iztok neighbourhood, for example, were inspired by Japanese Brutalism. Playing with shadow and referring to wooden structures, the buildings' crossed beams maximise the power of raw concrete.

The towers were designed in 1973 by Stefka Georgieva, who worked both in Nikola Nikolov's Sunny Beach team and at Glavproekt. Today, she is considered one of the most talented of Bulgaria's Brutalist architects, recognisable by the outlandish perfection of each of her creations. Her husband, civil engineer Levcho Manoilov, taught at the Institute for Building Construction and researched the usage of concrete, Brutalism's main ingredient. The Institute, on Hristo Smirnenski Boulevard, itself is an example of Brutalism.

The style was considered prestigious by the Communist regime, and was used for the Boyana residence (1978), the pièce de résistance of Bulgarian Brutalism. Todor Zhivkov himself lived in the compound, and Building No. 1 was used as the State Council. Today, it houses the National History Museum. The compound was designed by the studio of Aleksandar Barov, with Stefka Georgieva as lead architect and engineer Valentina Atanasova as designer of the surroundings – Bulgarian Brutalism paid a lot of attention to the connection with the outdoor space and nature.

Brutalism par excellence at the now crumbling Bankya Communist government residence

With their taller upper-floors, the buildings at Boyana residence look like oversized National Revival houses. Yet their size is counterbalanced by a refined use of an alternating pattern in concrete and a repetitive pattern of symbols. The inner courtyard of Building No. 2, which was used as a hotel for visiting dignitaries, reminds of a monastery. The interior of the buildings is lavish: large chandeliers, elaborated ceilings, sculpted wooden doors… Boyana breathes power. The buildings, the garden and the park join seamlessly: the residence is in perfect harmony with its surroundings.

Curiously, the imposing Unicredit Bulbank headquarters were not built until… the Communist regime collapsed. The design by Vladimir Romenski and Romina Romenska for what was originally Bulgaria's Foreign Trade Bank dates to 1970. Construction was finished in 1992; the swansong of Communist Brutalism in Bulgaria.

All over the world, organisations urge to preserve Brutalist buildings. Few, if any, of Bulgaria's Brutalist buildings are listed. Consequently, many have been demolished or are crumbling. Others have undergone modifications which annihilated their Brutalist nature, such as the painting and insulation of the Russian Centre.

However, some newer buildings are clearly inspired by Brutalism, like the Urban Module tower that was built in 2013 on Aleksandar Stamboliyski Boulevard in Sofia. In a way, the legacy of Bulgaria's Brutalist architects lives on.

*Mike Diliën, who has lectured and done research in Spain, Italy and Argentina, works for Belgian national health insurance