Well, what were they worried about? Fifty days to go and it's all over bar smoothing the sand in the long jump pit. But how did the Greeks, and Santiago Calatrava, turn a near disaster into a national triumph? We went to Athens to find out
The dust is finally settling over Athens.

For months the city has been deafened by the clangour of construction and blinded by the dust and fumes that have thickened the haze of smog above the most polluted capital city in Europe. And for months the world has stared in disbelief at the Greek workers as they raced to close the gap between where they were, and where they needed to be if they were going to actually host an Olympic Games in August. Indeed, the situation became so serious the International Olympic Committee threatened to move the games to another country if the roof of the main stadium was not in place by 20 May. Yet the Greeks have pulled off the impossible. After a last second flailing sprint for the deadline, they will be just about ready for the influx of athletes and spectators that arrive on the 13 August for the start of the centennial games.

The critics had good reason for thinking that Greece would struggle to host the games. This small, comparatively poor nation had an extraordinarily ambitious construction programme, including an airport, motorways, a tram system and extensions to the city's metro and suburban railway. Then there were the 38 venues for the games – including a landmark stadium designed by Spanish architect engineer Santiago Calatrava. Unfortunately for the Greeks, that structure, intended to be the glory of the games, came to symbolise all its problems. It was the most delayed project of all, thanks to the difficulty of building its roof. Not that the designer was worried. "I had no doubts at any time that it would be completed on time," says Calatrava confidently – now that he has been proven right.

A tour of the city reveals that things are now looking good. The airport is fully operational and the motorway flows smoothly into Athens – apart from a wobble at one unfinished interchange. The suburban railway line runs along the central reservation of the motorway and workers are finishing stations and putting in the overhead power lines for the trains. The only people present at many Olympic facilities are policemen standing guard over padlocked gates. And you can take the newly extended metro or the motorway without hiccup to the jewel in the crown, the Athens Olympic Sports Complex.

At the complex, workers are finishing off the main entrance. Inside, the most striking thing is the scale of the open spaces, white and empty and lit by intense Mediterranean sunlight. These are virtually finished; the fountains in the main plaza sit waiting to be filled, their blue paint a small relief from the glare. At the main stadium there is more activity – the area around the four great foundations looks like a traditional building site with brown earth extending well beyond the stadium itself. Right now it is being crawled over by landscaping teams – when the games open this will be a bank of trees and shrubs. Inside the stadium, preparations are being made for the opening ceremony in 50 days' time. Police and men in military fatigues sitting enjoying the sun in the spectator seats.

Although many of the facilities existed previously, Calatrava's masterplan has unified them along a new central axis complete with a sculptural wall (see page 26). And he has given the complex a distinctive architectural identity with new roofs to the velodrome and main stadium. The other buildings include an indoor centre for gymnastics and basketball, a tennis centre and an outdoor swimming pool – that was to have been an indoor swimming pool, but the roof was abandoned owing to lack of time.

The roof to the main stadium is virtually finished and looks magnificent. It transforms a plain, dull concrete bowl into something special. The roof has two parts, each with two tubular arches. The first sweeps high over the roof panels and the other passes just underneath. They converge at either end and are supported in only two places. The main roof follows the oval shape of the stadium and at each end a finger extends and delicately touches its neighbour.

Calatrava wanted this structure to capture the ethos of the games. "The idea of stronger, faster, wider and higher is embodied in the Olympic Games," he explains, "We hope the 100 m will be run 1000th of a second faster than last time. This is represented in the engineering; if one thing symbolises this idea it is the roof, as far as I know there is no other 304 m span across a stadium in the world. This is a great achievement."

Boasting might be justified now, but the reality was there was very little time to realise this grandiose vision. Athens was awarded the 2004 games in 1997 but ran into problems straight away. There was a struggle between politicians over control of the games – which the professionals avoid discussing – and then there was a clampdown on public spending designed to ensure Greece could join the euro. As a result, the organisers were not ready to start appointing designers until 2000. It took until 2001 for the Greeks to approach Calatrava and ask him to come up with the plan for the main complex.

At that point, even the Greeks were worried that there wasn't time to get everything done.

We hope the 100 m will be run 1000th of a second faster. This is represented in the engineering

Santiago Calatrava

"In June 2001 I presented to the former culture minister and showed what the Olympics could be," Calatrava says. "During this time many questions were asked about whether it could be built in time. I said to the minister it was possible, and it would be finished on time." Calatrava's persuasive skills must have been as good as ever, because he got the green light in October 2001.

By June 2002, the design had been prepared and the bidding process for the contractor had started. Five months later, Aktor, Greece's largest contractor, won. This job included the Athens Olympic Sports Complex. The win placed Aktor in a difficult spot: it had won other bids, including the Olympic Village, and it was desperately short of time. When it started work with Calatrava and the subcontractors in December 2002, it had just 18 months to complete the whole thing.

Aktor had trouble getting out of the blocks. "There were some significant changes at the beginning of the project," says Constantinos Mathiopoulos, Aktor's construction director of building projects. "For example, the diameter of the main tubes was made bigger in order to be safer and to conform to European codes." He adds that these changes theoretically added six months to the job. "These changes would have meant the project would have been finished at the end of 2004 – but we still finished on time."

What saved the games was a decision to use more prefabrication than originally planned. This included the secondary roof structure, which was bolted into position rather than welded on site. "In the first design Calatrava wanted to see a tube coming out from the main tube without bolts," says Mathiopoulos. "We changed this so it could be done in the factory. Although Calatrava wanted it done in one piece you don't really notice the difference."

Work finally began on site in March 2003, after the clock had showed just 15 months remaining. Calatrava always intended to build the two halves of the roof 70 m from the stadium and then slide them into position. This was to allow work to proceed simultaneously on the roof, and on refurbishing the stadium. Embarrassingly, the distance of the roof from the stadium proved a splendid photo opportunity for those who wanted to demonstrate how far from completion the project was.

Some engineers expressed concern about the wisdom of sliding such large structures. Chris Wise, who runs Expedition Engineering, carried out an assessment of whether the Greeks would be ready for the Olympics for The Guardian. His opinion was they could finish all the Olympic projects except the Calatrava roof – unless they were very lucky. "Nothing like this has been attempted before," he wrote. "I would say the whole thing is sufficiently risky that you would want a six-to-nine-month margin in case something goes wrong. But they have given themselves only 14 weeks for the final act, which strikes me as very optimistic."

At first it looked as though Wise was right.

The first date set for the big slide was 28 April, but this didn't happen. Calatrava blames the weather, which caused two weeks of delay.

"We are working in such a tight schedule that those two weeks were crucial." Frustrated, the IOC gave the team a final deadline of 20 May to raise the roof.

Simon Scheller, Calatrava's senior project manager, says he was unfazed by the atmosphere of gathering panic. "Sliding is a technique we have used many times to move bridges into place. To have invented something new – that would have been too risky. This was very simple: it's just a weight, and you pull or push it. If it was a complex technique the risk of it failing and destroying the roof would be too high."

Scheller's confidence was spot on, despite this being the largest structure Calatrava has ever attempted to move. Work started on sliding the first arch on the 10 May and was completed two days later. The second half of the roof was moved on 3 June, also without incident. The installation of the roof's polycarbonate cladding is well advanced and scheduled for completion in a week's time.

The citizens of Athens have their say

Elena Kaplina, artist
I believe the Olympics are good for Greece. It’s difficult economically but the whole world will look at us during the games, and afterwards with more attention.

There have been problems though. Greek people are not very disciplined. They leave things to the very last hour then work very, very hard. I am also like this and do things at the last minute. Things are not all ready but I believe they will be, if not they will be made to look ready.

I believe if someone puts in a lot, they take a lot out. They have spent a lot of money on the games but they will get a lot back because there is a new face for Greece. Maybe more tourists will come and think of Greece better in the future.

Andreas Zinelis, waiter
Although the cost of the Olympics is enormous it’s a good advertisement for our talents. It is also good for the infrastructure of the city. But we should have been better organised about the time and done things earlier. But these delays are part of our attitude and the Mediterranean culture.

I think it will be finished on time. I wish I could go to the opening ceremony but the tickets are very expensive.

The economy has problems but they are not due to the games. I think the government needs to be more effective with its financial policy.

Yiannis Kalaitzopoulos, businessman We were the first country to have the Olympic games so it is best that they are held in Greece. But I do worry about the crowds as Athens is a small city. There will be problems with traffic even if the roads are ready.

I love the new stadium. I used to play soccer there, now it’s like a new born stadium. The Greek people do everything at the last minute, but everything will be perfect and ready on time.

Whether it is worth the money depends on how successful the Olympic games are – if people come to see the games or will they be scared of terrorists. If it’s not successful we will pay for it for God knows how many years. But I think it will be fine – I hope so.

Andreas Stryfdarus, oil economist
The Olympics are very good. We love sports and we love our country. And everything is finished now. I am going to some events as my brother has bought tickets to several events.

The Greeks, we don’t care about the money; culture is more important. Maybe they have borrowed too much to pay for the Olympics, but other countries would have done the same thing; it’s not a Greek phenomenon. I have read that 95% of Greeks want the Olympics. The exception is the Communist party; they are officially against it. Also, the new tram, trains and roads are very good for us.

Olympic winner: Calatrava on his stadium

Now the Olympic Stadium is virtually finished, Santiago Calatrava can relax, and enjoy the publicity the project has brought him. It has turned him into an international star, along with Frank Gehry, Norman Foster and more recently Daniel Libeskind. At a press conference last week in Athens, photographers and journalists from newspapers all over the world were elbowing each other out of the way to get a picture or ask a question of the great man, Calatrava appeared completely unfazed by all this. When asked how much the project had cost the reply rolled off his tongue like a hardened politician. “We can answer this next week with the client,” he said, to laughter from the press.

The Olympic Stadium is not this architect–engineer’s first Olympic commission; one of his earliest jobs was designing and building the Bach de Roda Bridge for the Barcelona Olympics in 1984. This kicked off a successful bridge building career – examples include the Alamillo Bridge in Seville, the Campo Volantin Footbridge in Bilbao and the Bridge of Europe in Orleans. Looked at in this light, the roof is, essentially, another bridge. Many of the elements are borrowed from bridge building – for example, its upper structural arch is linked to the lower tube by cables and the structure is supported at both ends, just like a bridge.

Calatrava says there are three main sources of inspiration for the Olympic Stadium. The first is Classical Greece, this is seen in the layout of the masterplan with its classical agora, main axis and plaza (see map). The second is a later Greek tradition, the Byzantine with its arcs and vault, visible in the roofs of the stadium and the velodrome. Finally the location of the games is pivotal to Calatrava. “The open spaces and all the aspects of the landscaping have a Mediterranean character,” he explains. “We have used ceramics, stones and plants related to the area and planted thousands of bushes and trees.” The colours are Mediterranean, too, mostly white with flashes of blue. And of course there is Calatrava’s strong architectural stamp visible in the sculptural lines of all the structures, his trademark organic, curvilinear shapes that are most powerfully evoked in the sculptural Nations Wall.

How the roof was built

One of the most striking aspects of the stadium roof is its delicate balance. Each half weighs 9000 tonnes yet is only supported in two places. This is possible because the weight is evenly balanced on each side of the main arches supporting it. Because the roof follows the oval shape of the stadium, it projects from the main structure by 70 m at the ends and 45 m in the middle. The lower main tube on each side of the roof is a “torsion tube”; this is designed to resist twisting forces in the structure caused by the wind and possibly earthquakes. The upper tube carries the weight of the roof. Cables join the two arches to brace the structure and transfer the loads. Perpendicular ribs are attached to the lower arch and these support the roof panels.

Each arch is made up of tubular segments up to 3.65 m in diameter, with tube wall thicknesses of up to 80 mm. The roof has been designed so people can walk inside the tubes – the upper arch even has stair inside to help at the steeper ends. “The view from the top is incredible,” says Simon Scheller, Calatrava’s senior project manager. Access to the structure means it can be checked by security for bombs prior to events.

Five towers were erected to construct the arches. First, arch segments were lifted up into each tower and orientated so they were in exactly the right position. Next, segments were welded together on the ground then craned so the ends met up with the segments in each tower and welded together. Once the arches were complete the transverse ribs were bolted on, cables installed and some of the roof panels fixed in place. Scheller says the work could have been completed faster but only at the risk of compromising health and safety. He says only the welders worked at night as the big welds joining the tubes had to be done in one go.

The two arches join at the ends and were built resting on Teflon-coated stainless steel “skis”. These sat on rails that would guide the roof on its journey to the stadium. Eight hydraulic jacks were used to move the first arch but only four were needed for the second. “The friction factor was much better than we calculated,” comments Scheller. Mathiopoulos says the two arms at the end of the roof were in exactly the right place and joined together perfectly.