It was larger than Wembley Stadium, taller than the Statue of Liberty and three times heavier than The Brooklyn Bridge.
But the enormous, 35,000 tonne structure was what was needed to finally enclose the scene of history’s worst nuclear accident, and seal in what is still regarded as the most dangerous waste anywhere in the world.
Ever since the Chernobyl disaster in 1986, when plumes of radioactive dust smoke threatened to cover the whole of Europe and beyond, Soviet authorities had tried to clean up the site.
The effort to avert catastrophe on a global scale, and the horrendous effect of radiation on those who came into contact with it, is vividly depicted in hit Sky/HBO series Chernobyl.
But despite a hastily constructed concrete structure to contain the site built in the immediate aftermath of the explosion, the nuclear plant near the town of Pripyat, Ukraine, was still leaking dangerous levels of radiation.
Thirty years on, in November 2016, Chernobyl’s ground zero was finally made safe when the entire disaster site was encased in a new sarcophagus designed to seal the site for at least the next 100 years.
Called the New Safe Confinement, the tomb was such a feat of engineering that when it was first suggested in the 1990s people thought the idea of building something so big in one of the world’s most hazardous places could never be done.
The first effort to seal off the disaster zone, in the days and weeks following the Chernobyl explosion, is believed to have cost an unknown number of lives.
In total, around a million men from across the Soviet Union were brought in to help with the initial clean-up and containment.
Helicopters dropped sand and lead over the reactor to extinguish the flames and coal miners were drafted in to dig underneath the reactor’s core, to cool the nuclear fuel with liquid nitrogen.
It took 206 days to build the first sarcophagus, using 400,000 cubic metres of concrete and 7,300 tonnes of metal framework.
Yaroslav Melnik, the leader of a group of firefighters brought in from the town of Ivano Frankivsk, remembered: “We worked in three shifts, but only for five to seven minutes at a time because of the danger.
“After finishing, we’d throw our clothes in the garbage.”
Later named the ‘liquidators’, thousands of these men and women are reported to have died during their work, or suffered long-term illnesses from acute radiation exposure.
But the first tomb was never supposed to last, and after Ukraine gained independence after the collapse of the Soviet Union in 1991, the country launched an international competition for ideas about how to make Chernobyl safe again.
It was won by a French consortium with a plan called “Resolution”, which involved encasing the entire Soviet-built sarcophagus with the damaged reactor inside it within a whole new structure.
But the task was huge, as the new sarcophagus needed to be built next to the highly-radioactive site – where radiation levels are 20 times more than a lethal dose – then moved to its final position, without risking the safety of the workers.
The project would cost more than £240million.
Vince Novak, director of nuclear safety at the European Bank of Reconstruction and Development, who oversaw the project, said the first challenge once they began working in 1999, was to shore up the existing structure to stop it from collapsing.
They found that the original sarcophagus was so precarious that it could have collapsed at any moment, risking another Chernobyl disaster.
He said: “The Soviets had lowered the beams into that sarcophagus using helicopters and the whole structure of the roof was in fact built the same way, using helicopters.
“Pieces had been dropped in one by one and not tied together.
“They were just sitting there and what quickly became apparent was that either these beams were sliding or that the wall was moving.
“It came to a point where further movement of an inch or so would have led to the huge beams falling down. You would have a collapse of the shelter.”
The segments of the sarcophagus were built and pre-assembled in Italy, then shipped by sea to Ukraine, then transported by road to Chernobyl.
It took 18 ships and 2,500 trucks to get all the parts on site, before the structure was assembled, a task which took more than two years.
To minimise exposure to radiation for the workers, the huge structure was erected 300m away from the accident site and then moved it into position.
The sarcophagus included advanced ventilation systems and remote controlled robotic cranes that would dismantle the existing Soviet-built structure and reactor once the new one was sealed.
When the building was finally moved into its final resting place on 29 November 2016, it was the largest object ever moved by people.
Over 100,000 people were involved in this second effort to make the world safe from the continuing threat of Chernobyl. Finally, 30 years and seven months since the explosion, the reactor was finally declared safe.