Italy's culture ministry said that it is investigating reports that bits of rock have fallen from the Colosseum.
Witnesses reported seeing the fallen masonry on Sunday.
Italian news agency Ansa reported another bit fell on Tuesday, but Colosseum director Rossella Rea denied it and blamed the false report on a "psychosis" that occurs every so often that Rome's stadium is crumbling.
Italian environmental group Legambiente has frequently raised the alarm about the precarious state of the Colosseum, charging that car exhaust fumes and vibrations from vehicles and a nearby subway are damaging the Colosseum's travertine exterior and brick and tufa interior.
A 25 million euro restoration, paid for by Diego Della Valle, founder of shoemaker Tod's, is set to begin in March.