Rome may be at risk of a dormant volcano erupting which is slowly reactivating, scientists have said.
After a series of earthquakes hit central Italy over the past two months, experts say there is no risk that the capital city will be hit by a "big one" but a volcano located nearby is showing signs of activity.
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According to the Daily Telegraph, an eruption is about a thousand years away but chambers under the residential areas of Ariccia, Albano and Castel Gandolfo are filling up with magma and the ground is rising by up to 3mm per year.
In a study published on Geophysical Research Letters, scientists said the main concern is the long pauses between activity.
Fabrizio Marra, from the National Institute of Geophysics and Vulcanology, told La Republicca: "When the eruption happens, it has an explosive effect, like opening a champagne bottle after shaking it."
He added: "This sort of process has, for example, caused the string of earthquakes that hit this area at the beginning of the 1990s, with minor quakes and a few cases of magnitude four quakes."
Meanwhile, the 6.5 magnitude earthquake that shook Italy on Sunday is threatening Rome's Colosseum.
Francesco Prosperetti, the special superintendent for the Colosseum and the Roman Forum, told Corriere della Sera that "with the earthquake the cracks are increasing".
Officials carried out an inspection of the site following Sunday's quake.
Alessandro D'Alessio, an archaeologist, told Corriere Della Sera: "The (Colosseum) arches are the best structures to absorb movements and vibrations. The ancient Romans knew the earthquakes of the Appenines well."
Around 11,000 people are expected to need help from Italy's Civil Protection agency following three powerful earthquakes that hit the country.
The 6.6-magnitude quake that hit on Sunday morning was the most powerful yet. No one was killed, but it destroyed a Benedictine cathedral, a medieval tower and other landmarks in a mountainous region of small historic towns.
Italian Premier Matteo Renzi said the nation's "soul is disturbed" by the series of quakes. It started with the deadly event on August 24 that killed nearly 300 people.
There were two powerful aftershocks on Wednesday. Then on Sunday the strongest earthquake felt in Italy in 36 years hit.
Renzi vowed to rebuild houses, churches and business, saying, "a piece of Italian identity is at stake at this moment".