“It could collapse at any time,” says the architect and activist Wassim Naghi. The facade of the unfinished, subterranean space museum in Tripoli, Lebanon, is visibly decaying and its steel reinforcements are rusted – but that may not be its biggest problem. “The ageing concrete’s carbonation is invisible,” explains Naghi when we meet in his office in the centre of the city. “We don’t know how bad it really is.”

Situated beneath an elevated concrete helipad, the museum was part of a planned permanent international fair designed by the Brazilian architect Oscar Niemeyer in the early 1960s that was expected to accommodate more than 2 million visitors a year. The 100-hectare (250-acre) site’s 15 existing buildings also include a domed theatre, an atrium, an arch and collective housing. A 717-metre-long boomerang-shaped canopy was designed to house the permanent exhibition, alongside a separate, traditionally styled pavilion for exhibitions relating to Lebanon.

But the country’s 15-year civil war halted the project in the mid-1970s and today, the abandoned fairground stands empty save for joggers, dog walkers and occasional tourists.

Some of the highlights of Niemeyer’s expo site including the Lebanese pavilion, bottom left. Photographs: Chantale Fahmi/Walid Rashid Photography/Alamy

Decades of neglect have endangered the fair’s structures and Naghi is leading the campaign for its restoration. In 2016 the basement ceiling of its atrium collapsed, in part due to mistakes made in the initial construction of the building.

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The fairground, a major urban development project for the city, was part of a decentralisation policy adopted by then-president Fouad Chehab. Niemeyer came to Lebanon in 1962 and spent a month in Tripoli. “He was terrified of flying and travelled by boat,” says Nazih Taleb, whose consultancy developed the technical drawings and construction plans for the fairground. As well as the existing buildings, the preliminary sketches included a playground, a bowling alley, housing and shops.

Niemeyer’s designs for the Tripoli fair were modelled on Brasília, but he also experimented with new structures

Niemeyer, who designed some of the 20th century’s most iconic modernist buildings, is best known for his work on Brasília, a futuristic planned city built in the 1950s to serve as Brazil’s new capital. The Pritzker prize-winning architect, a communist, sought exile in Paris during Brazil’s military dictatorship, and designed the French Communist party’s headquarters. A defining feature of Niemeyer’s architecture was his use of curves on reinforced concrete, inspired, he said, by the female figure. But towards the end of his career, modernist development projects such as Brasília were criticised as examples of utopian over-planning.

The fair’s amphitheatre and arch. In September the fair site was placed on Unesco’s list of properties being considered for nomination to its world heritage list. Photograph: Walid Rashid Photography

Niemeyer’s designs for the Tripoli fairground were modelled on Brasília, but he also experimented with new structures for the space museum and the theatre beneath the dome, which was meant to have a rotating stage. “The Lebanon pavilion’s pointed arches are the fair’s only reference to a vernacular architecture,” says the architectural historian Farès el-Dahdah of Houston’s Rice University. Taleb says: “The curved structures were technically complex to build, and Niemeyer insisted that we maintained the exact curvature of his original drawings.”

The location chosen for the fairground was an area of orange orchards south of Tripoli. Odette Sawaya, whose house in the 60s stood at the edge of the city, then known for its fragrant orange blossoms, recalls a visit from ministers involved in mapping the fairground: “We went out on to the balcony so they could assess the grounds. All you could see were the orchards and the sea.” The scent of orange blossoms has been lost due to extensive urban development of the city, and today Sawaya’s balcony overlooks a multi-storey concrete apartment block.

Brasília was built in under four years, but the fair – mired in issues over land appropriation, construction mistakes and inflating costs – took more than a decade. Niemeyer expressed his concerns about the delays in a letter to the Lebanese government in the early 70s. After the country’s descent into civil war Syrian forces occupied the complex until the late 90s.

Left: an old postcard of Tripoli’s orange orchards, part of which were used for the international fair site. Right: The fair’s general manager inspects construction progress, in about 1967. Photographs: private collection/Wassim Naghi

The marginalisation of Tripoli, whose historical port was once more important than Beirut’s, also contributed to the fair’s decline. A Chinese company’s proposal to lease the site and turn it into a trade fair for Chinese products in the Middle East was dropped in 2007 due to security concerns. That year, the Lebanese army entered into a three-month conflict with Islamist groups living in the nearby Nahr el-Bared refugee camp.

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Ongoing violence between the suburbs of Bab al-Tebbaneh and Jabal Mohsen was compounded by the fallout from the war in neighbouring Syria. About 70,000 refugees from Syria live in the city and 9% of its residents are unemployed. “Had it been in any other city in Lebanon, the fair would have had more support from the government,” says Naghi.

With the local conflict now over, residents, civil society groups and international agencies are actively trying to restore the city’s dynamic and change its public image. “It’s the liveliest it has ever been,” says Nadine Dib, who set up Warche 13, a creative space and cafe in Mina, the old port district, in 2016. Since June, two contemporary art exhibitions organised by local and internationally based organisations have taken place in the site’s buildings.

The newly created Tripoli special economic zone has secured a lease on part of the fair’s undeveloped grounds to build a tech hub and will launch an international tender for proposals for the development. Two buildings – a customs house and an administrative office – will be renovated.

The helipad, lit for the opening of the 2018 Cycles of Collapsing Progress exhibition. Photograph: Walid Rashid

The city’s revival could help raise funds for the fair’s restoration. In September the fairground was placed on Unesco’s list of sites being considered for nomination to its world heritage list. With EU funding, the fair’s guesthouse was restored and reopened a couple of months ago as a workspace for local carpenters.

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Nonetheless, the restoration challenges are immense. Naghi estimates that up to $40m (£31m) is needed to treat the concrete and make it safe again. “Lebanon has no regulations for protecting modern architectural heritage,” says Dahdah, “so conservation is a moot question.” In the early 2000s, the fairground’s collective housing unit was converted into a chain business hotel. “It’s completely out of touch with the building’s original design and function,” says Naghi. It also reduces the chances of the site obtaining world heritage status.

A further challenge will be reconnecting local residents with the abandoned site. Today its borders are surrounded by walls built by the Lebanese government to restrict public access. “Many Tripolitans remember the fair as a base for the Syrian occupation,” says Dib, “and don’t know its architectural significance.” Naghi adds: “For residents, it is a broken promise.”

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