Rome's ancient Colosseum is leaning and needs urgent repairs but the long-delayed restoration project has been pushed back to December, the site's director says.
Experts have discovered that the former gladiator battleground is tilting about 40cm on its southern side, possibly because of cracked foundations, sparking fresh fears the 2000-year-old monument may be falling apart.
"It could be due to several factors: flaws in the original construction - though 40cm is rather a lot for that case - or problems with the foundations," the Colosseum's site director Rossella Rea told AFP on Monday.
The landmark Roman amphitheatre, which is at the centre of a busy intersection, has been dogged by problems in recent years. Chunks of the arches fell off in December last year, and there were similar reports of damage in 2010.
Rea has appointed Italy's Institute of Environmental Geology (IGAG) and La Sapienza University in Rome to explore possible reasons for the tilt. Their findings are expected to be published in about a year.
News of the tilt came as Italy's cultural minister prepared to unveil the latest timetable for the Colosseum's long-awaited restoration on Tuesday.
The restoration works have been delayed by a series of protests by trade unionists over Italian tycoon Diego Della Valle's plans to clean up the dirt-streaked arena.
In January, the billionaire threatened to pull 25 million euros ($A29.53 million) in financing following investigations into alleged irregularities.
The three-year restoration project, which aims to increase by a quarter the areas to which tourists will have access, was supposed to begin in March. It was postponed to July and is now unlikely to start before the end of the year.
"If everything goes as planned, we'll be able to begin in December ... unless there is another appeal" to halt the project, Rea said.
Designed as a 50,000-seat amphitheatre and completed in 80AD under the Emperor Titus, the Colosseum was used for gladiator contests and mock sea battles. It is considered a masterpiece of Roman architecture.
Over the past decade, the number of people visiting the site annually has jumped from one million to about six million - largely thanks to Ridley Scott's 2000 epic film Gladiator, starring Russell Crowe.
Rea downplayed the latest outcry over the arena's condition, insisting that the tilt may not be new and has yet to be closely studied by experts.
"It's a recently discovered trait which will be monitored to see if the lean advances over time," she said. "It doesn't worry us."
Rea dismissed other expert theories which say heavy traffic is causing irreversible damage to the Colosseum.
"It's not true, because that part of the monument is not exposed to traffic," she said.
