ROME (Reuters) - All roads might lead to Rome, but when they reach here, they are likely to be dug up, shut off or under renovation as the city undergoes a monumental facelift ahead of the 2025 Roman Catholic Holy Year.

The Vatican expects up to 32 million tourists will descend on the Italian capital for the Jubilee, putting Rome's antiquated infrastructure under enormous strain.

But taking advantage of the event, a special celebration traditionally held every quarter of a century, Rome has pooled billions of euros of state and European funds to overhaul tourist sites, transport hubs, parks, streets and even its rubbish bins.

The frenzy of work has snarled traffic, to the fury of residents, and left some visitors this summer feeling short-changed as they weave their way through myriad building sites, but Mayor Roberto Gualtieri promises it will all be worth it.

"This is an unmissable opportunity to make structural changes ... and transform Rome," Gualtieri told Reuters this week. "We are going to get a more sustainable, inclusive and innovative city that enhances its extraordinary heritage."

A record 3,200 public construction works are under way, he said, including 322 projects that are deemed essential for the Jubilee, such as the creation of what Gualtieri promises will be "one of the most beautiful squares in the world" by the Vatican.

The scheme involves shifting a major road junction underground and workmen are pulling overnight shifts to complete the project by Dec. 24, when Pope Francis is due to open St. Peter's bronze Holy Door and inaugurate the Jubilee.

During a Jubilee, Catholics can obtain special indulgences, or remission of their sins, if they fulfil certain conditions and do good works or make pilgrimages.

The city council has marshalled 1.3 billion euros ($1.4 billion) in special Jubilee funding from the state as well as some 3 billion euros from post-pandemic EU funds.

It has also put together financing for a further 4 billion to complete Rome's third metro line, which will connect the city's two main basilicas -- St. Peter's and St. John Lateran -- and dissect the heart of the art-rich centre.

DIGGING DEEP

One of Rome's busiest squares, Piazza Venezia, has been largely closed to traffic since the start of the year as a specially designed, 185-tonne hydro cutter begins digging an 85-metre deep (280 feet) ring that will eventually encase the new Metro C station, just down the track from the Colosseum.

Before any serious construction can start, workers will have to sift through the top 20 metres of earth, which is known to contain archaeological remains, while ensuring that nearby churches and palazzi don't suffer subsidence.

Underscoring the old adage that Rome wasn't built in a day, the Piazza Venezia station will not open for a decade.

"It is true that 10 years seems like a lot compared to the timelines for work in Madrid or London, but it is also true that in these stations we are not only handling the engineering but also the archaeology," said project manager Andrea Sciotti.

The existing metro lines are undergoing major renovations to ensure they can handle the expected crowds, with two of the busiest stations, including that serving the Spanish Steps, about to close for a revamp.

The city is temporarily replacing trams with buses to allow for work on a new tram depot, while visitors arriving at the main railway station are greeted by mesh fencing and clouds of dust as the adjoining bus terminal gets a badly needed new look.

The intense activity has also engulfed tourist attractions. All of Piazza Navona's three fountains, including the celebrated Fountain of Four Rivers, are boarded up for restoration, likewise the Renaissance fountain in front of the Pantheon.

"We knew work was going on, but we didn't realise there would be quite so much. It is a bit of a bummer," said Tom Pagano, a tourist from Sacramento, California, visiting a sun-drenched Rome with his wife and daughter .

"I guess there is so much to see here that you can always find something that isn't covered in scaffolding," he added. ($1 = 0.9239 euros)

(Reporting by Crispian Balmer; Editing by Keith Weir)

By Crispian Balmer