When the Olympic Games open in Athens on Friday, they will be more than just a test of athletes.
The venues have been swept for bombs and locked down
One of the biggest challenges is whether the first Games since the 9/11 attacks can pass off safely, despite the threat of international terrorism.
The Greek government has thrown everything into securing the city, spending more than $1.2bn on security - three times what was spent on Sydney 2000.
A Nato force is on standby, Patriot missile batteries stand ready to down rogue aircraft while a network of cameras co-ordinate the efforts of 70,000 police, soldiers and emergency workers.
Prime Minister Costas Karamanlis has declared the Athens Games will be safe from terrorism - or as safe as is "humanly possible".
Even critics of the government's massive security operation are declaring Athens "one of the safest places on Earth".
In the centre of the city, there is a highly visible security presence, with armed police on street corners, at subway stations and outside luxury hotels.
THE SECURITY BLIMP
59m (200 feet) long
Contains 6,000 cubic feet of helium
Flies at 1,200m (4,000 feet) and carries 13 people
Carries high-resolution cameras that can work at night
Detects unexpected changes in image patterns
Sniffs air to detect chemical attack
Will float for hours even after punctured by bullets
At Piraeus port - where thousands are staying on cruise ships in the harbour - special security measures are also in place under the auspices of Athens' specially created Olympic Games Security Division.
Underwater sensors have been deployed to detect divers in the harbour; coastguards in high-speed boats with infra-red and CCTV cameras are patrolling the waters.
On the bustling road along the harbour's edge a gated security fence deters those without tickets from trying to board any vessel.
The Olympic venues themselves have been swept for bombs and are locked down.
Athletes from high-risk nations like the United States, Israel and Britain have been afforded armed guards. Security searches for spectators will be rigorous, officials say.
In the run-up to the Games, intelligence officials say there have been no indications that the world's largest sporting event will be a target for terrorism.
Nevertheless, there have been a number of minor incidents, quickly blamed on domestic left-wing extremists, or anarchists.
Surveillance is so heavy it has sparked accusations of overkill
Less than a fortnight ago, a petrol bomb was thrown at the interior ministry in what was thought to be a protest at the security crackdown.
Indeed, there has been some disquiet at some of the measures, particularly the airship that is now hovering above the city for up to 16 hours per day.
The Democratic Rally rights group has gone to court to get the blimp banned, saying it could be used to eavesdrop on private phone conversations and even record details of people's everyday lives.
The police strongly deny this - and say security measures have been put in with full respect for human rights.
But the surveillance network does give them extraordinary abilities to track suspect vehicles and individuals.
The main goal is to "conduct the Olympic Games in an absolutely secure environment", the ministry of public order says.
But Mary Bosi, professor of international terrorism at Athens' Panteion University, says Greece has overspent: "We have done too much - more than is necessary. The government have panicked because of international pressure.
"Greece right now is the safest place on Earth. But for international terrorists, I don't think the Games are a target. Unpredictability has been their hallmark. Where is the surprise in attacking Athens?"
Athens is taking no chances.
As Prime Minister Karamanlis was quoted as saying in a recent interview with Time magazine: "One might say that some of the things said or done may border on excessive, exaggeration or sometimes hysteria.
"But one cannot dismiss a legitimate concern. So the only answer is: Try it. It's secure. All that had to be done has been done."
1 - Nato Awacs surveillance planes patrolling the skies listening for intelligence chatter
2 - Ships from the Greek navy, Nato and the US 6th fleet patrolling the sea
3 - Helicopters on constant surveillance over the city
4 - Gunboats sweeping harbour areas, especially around the VIP accommodation in Piraeus
5 - Greek special forces, backed by thousands of regular troops, placed in and around Olympic venues
6 - 70,000 police and security officers on duty
7 - Sensors to detect a chemical, biological or radiological attack placed around the city
8 - Surveillance airship patrolling the skies