Just a few hours before the glittering opening ceremony of the Olympic Games in Paris on Friday, a handful of arson attacks paralyzed the French railway system. Though there were no injuries, the apparent act of sabotage was a stark reminder of how vulnerable the biggest sporting event in the world can be. Read on for answers to what France is doing to maintain security as the host.

Why has there been such heavy investment in security?

France has repeatedly been the target of major terrorist attacks in recent years. The assault on the satirical magazine Charlie Hebdo in January 2015, followed later the same year by those on the Bataclan music club and the Stade de France, are particularly painful memories.

Then, in 2016, a terrorist drove a truck into a crowd in Nice. Recent years have seen lone perpetrators carry out more attacks, such as the knifing of a German tourist on a bridge over the Seine in Paris in December 2023. French authorities are therefore on high alert when it comes to the challenge of securing the world's biggest sporting event.

Are the borders being controlled?

In principle, France's borders with other signatories of the Schengen Agreement can be crossed freely. However, major events such as the Olympics are considered to be a justified exception to this rule.

This is the case now, with the borders between Germany and France set to be controlled from July 20 to September 30, a window that will also cover the Paralympics, which kick off in late August.

Who is allowed to attend the Olympics?

While it's difficult to maintain complete oversight, there is an accreditation process for anyone traveling to the Olympics as an athlete, official, companion, journalist, sponsor or in a similar role.

French authorities checked almost a million applications in advance — and rejected nearly 4,000. Reasons included links to radical Islamists, suspicions of foreign espionage or concerns about cyberattacks, according to French Interior Minister Gerald Darmanin.

Among the rejected applications were people from Russia, Belarus and other countries who wanted to be accredited as journalists or technical staff, though none were found to have concrete plans to carry out attacks, the ministry said.

How are security measures affecting residents and visitors?

More than 45,000 security personnel have been deployed in the French capital to protect the peace, with the city divided into security zones. The gray security zone, which is located directly along the Seine, can only be entered with a permit.

The extended red zone can be entered freely by pedestrians, but vehicles require a permit called a "Games Pass." Residents or professionals are eligible for the pass, but must always have a QR code ready to identify themselves as a holder. This means that some residents need a QR code to reach their own home, a situation that has led to some criticism.

What are security forces looking out for?

The opening ceremony took place in the Paris city center, where the athletes traveled along the Seine on boats instead of their traditional march into the stadium. This went smoothly on Friday, partly because the number of spectators was reduced before the start of the ceremony.

But with sporting events taking place across the densely populated city, security forces are also using helicopters, drones and cameras supported by artificial intelligence, among other things, to maintain oversight. Divers and snipers have also been employed to secure many places around the city.

It's not possible to fully secure the French rail network to prevent every act of sabotage. But a comprehensive security system quickly detects external disruptions and sets all signals to red to protect passengers — as they did on Friday.

This article was originally written in German.