Fighter jets, a naval destroyer and guns on show: 'Unprecedented' security operation for Pope's funeral

As the line of mourners moves slowly along behind him, Ciriaco Sarnelli peers at me from beneath the immaculate brim of his cap.

The military police chief looks, by any standards, magnificent - shoulders back and proudly wearing the black uniform of the Carabinieri. "Our history goes back more than 200 years," he says.

"We remember our past, and our place. The only people with black uniforms are the priests, the judges and the Carabinieri." He leaves the rest unsaid - the Carabinieri sit at the heart of Italian cultural life.

Pope Francis funeral: Watch and follow live Once, they defended the borders of a young nation. Now, they have a new challenge that has its own weighty burden - to keep St Peter's Square safe during the funeral of Pope Francis.

This is no easy task. Hundreds of thousands will descend upon the Vatican for the event.

Many of the world's best-known politicians and dignitaries will be welcomed into St Peter's Basilica. Inside will be Donald Trump, Sir Keir Starmer, Joe Biden, Emmanuel Macron, Prince William and dozens upon dozens of other dignitaries.

Outside will be the Carabinieri. They won't be alone - there are thousands of other police officers due to be assigned to protect the event - but the Carabinieri are affiliated to the military; the most highly-trained officers on duty.

Read more:How Pope's funeral will unfoldFull order of servicePope's doctor reveals pontiff's last regretCardinal who will be in conclave says picking pope is 'intimidating' "This is an extraordinary operation," says Sarnelli, as we look out over the crowd. "So we have employed some special units that belong to Carabinieri - the bomb squad, a dogs unit, snipers and helicopters.

We want to assure the people who are arriving here that they can take part in this event in the best way, in a secure way." He says they are ready for "common crimes" - like pickpockets in the crowd - but also "the biggest, terrifying events". He says there is "excellent coordination" with police forces from other countries.

Around him, his officers are smiling, chatting to tourists and Romans alike. The security here is overt but friendly, even if I'm told there are also plenty of plain-clothed officers mingling within the crowd.

Guns and grins both on show. A police helicopter circles above.

In the port of Rome, a naval destroyer has been primed for action; there are fighter jets ready to take off. You can watch full coverage of the funeral live on Sky News from 8am If the impression is relaxed, the reality is different.

The classic swan. All the strands are pulled together from one place and, what's more, it offers a perfect view of Vatican City.

From where I'm standing, I can see the front of St Peter's Basilica, the side, and the roads around it. I can see the crowds coming in, and the crowds going out.

And I can see an anxious policeman drumming his fingers. But we are not in St Peter's and not even in the Vatican.

This is the high-security control room on the fifth floor of Rome's police headquarters. And from here, you can see everything.

An array of screens are in front of us and, watching them, men and women, huddled over screens and all wearing contrasting uniforms. Some are military, some national police, some wear the clothes of firefighters.

A few are in plain clothes and there is even a man wearing the badge of the prison officers' service. This centre is a hub for collaboration and decision-making and it brings together every service that is involved in ensuring the safety and security of the funeral.

There is a Carabinieri officer here, as well as the Guardia di Finanza national police and the Roman force. The government's secret intelligence service is represented here, too.

Elisabetta Accardo is from Rome's police department. We talk against the gentle hubbub in the control room, colleagues pointing at screens and agreeing plans.

I ask when Italy last had to deal with a security operation on this scale, and she laughs. "Hundreds of years," she says.

"It is unprecedented. The level of security is at the maximum." She describes the plan as "structured three-dimensional security".

It is a plan that has been long in the making, but which has been reshaped over the past few days to react to the whims of the Pope's final wishes. It is, after all, more than a century since a pope was buried outside the walls of the Vatican.

You get the impression that the people designing the security plan could rather have done without having to add an hour-long procession through Rome into the plan. But so be it.

By Saturday night, it will be done. Rome can start to get back to normal; the foreign leaders will be on their way home.

And the Rome police will breathe just a little bit easier..