Euro 2016 kicks off on Friday when hosts France face Group A opponents Romania at the Stade de France amid an unprecedented security operation.
France remains under a state of emergency after last November’s attacks on Paris,when 130 people were killed.
More than 90,000 police, soldiers and private guards will be deployed at the tournament, with seven million fans expected to visit the 10 host cities.
The US and British governments have both warned fans they could be at risk.
But organisers Uefa, and the French authorities, insist they have done everything possible to keep the 2.5 million spectators expected at the 51 matches safe.
France faced its first major security test when DJ David Guetta performed on Thursday at the 90,000-capacity fan zone at the foot of the Eiffel Tower.
Paris alone will have a security force of at least 13,000 to patrol two zones and two stadiums, with the country’s state of emergency allowing police extra powers to conduct searches and put people under house arrest.
France coach Didier Deschamps, whose side were playing Germany in an international friendly when the Stade de France was targeted by suicide bombers, says November’s attacks evoked “very strong emotions”.
“We lived through some tragic moments,” he said. “So it will remain with us, even if with time we can think about it a little less.
“Today to have zero risk doesn’t exist, sadly, but we have to go forward and these Euros have to be a festival of football and festival has to be as beautiful as possible.”
Richard Walton, the Metropolitan Police’s former head of counter-terrorism, said the threat to Euro 2016 is “more acute than for any other international sporting event in history”.
A reported 500,000 British fans will be among the seven million supporters in France, and the British Foreign Office has warned that stadiums, fan zones and transport hubs are possible targets for attack.
England goalkeeper Joe Hart insists players will adhere to the advice of security officials at the 24-team championships.
Hart, 29, said: “We’re a team of footballers but we’re a group, we work together with the security and press officers, everyone’s got their various jobs and I’m very confident on everyone completing them.”
France’s junior minister for sports Thierry Braillard has said official fan zones are the only outdoor public spaces where screens will be installed, with bar and restaurant owners told not to host large outdoor TV broadcasts.
He added: “We can’t accept unorganised gatherings because police forces don’t have the means to secure them.”
Paris is just one of nine host cities preparing for the tournament, with games also taking place in Bordeaux, Lens, Lille, Lyon, Marseille, Nice, Saint-Etienne and Toulouse.
Jean-Christophe Bouvier, the Defence Secretary for the Lille region, says 200 security staff will be inside the city’s fan zone with 3,400 police and military forces working each day and hundreds extra on call if needed.
President of the Lille region Damien Castelain said: “It’s a very secure place in the fan zone.
“It’s easier to secure one place like this one than have people going to several places where it would have been impossible to make people safe.”
Mat Bastard, Lille’s Euro 2016 Ambassador, added: “If France win it’ll be so, so good, but my first victory is everything is well and everyone has fun.”