A slab of ancient lime plaster fell off the Colosseum, one of Rome's most popular tourist sites, on Sunday but visitors were not at risk, officials said. 'Around 6:00 am (0400 GMT) three plaster fragments came undone from the gallery of the central aisle of the amphitheatre near the equestrian statue,' a statement by the city's archaeological department said. Despite the incident involving a piece of less than one square metres (11 square feet) the Colosseum will remain open to the public. Humidity and temperature changes may have loosened the plaster. The government of Prime Minister Silvio Berlusconi is currently winding up restoration work on the iconic structure, which is depicted on Italy's five euro cent coins, ahead of next year's 150th-anniversary celebration of Italian unification. The Colosseum, which seated up to 75,000 people, took about 10 years to build and opened in 80 AD under emperor Titus, mainly as a venue for gladiatorial contests and public spectacles. It sits between the ancient Forum and the Domus Aurea, or Golden House, the palace of Roman emperor Nero, where about 60 square metres (645 square feet) of an ancient gallery collapsed in March, causing no injuries. Water seepage likely led to that collapse. Nero had the sumptuous villa built over an area of some 80 hectares (200 acres) in 64 AD after most of Rome was destroyed by fire while he himself, according to historians, played his fiddle. The extravagance of the villa became an embarrassment to Nero's successors, and they had it covered over by earth to make way for later Roman landmarks -- like the nearby Colosseum -- but in doing so, ensured its survival for the admiration of later generations. 