As tourists milled around the 2,000-year-old arena yesterday, restorers were hard at work on scaffolding above their heads, scrubbing under the arches with tiny brushes after hosing down the ancient travertine stone.
A fine spray of water is gently fired at the stone and since the £8 million project started last September the work has seen charcoal black crusts from car fumes disappear.
Colosseum director Rossella Rea said: “The surprise is the colours underneath. The travertine is not white, but mixes hints of pink, yellow, red and brown, the colours that come with ageing.”
Cinzia Conti, technical director of the monument, said the stone once again boasted the hues it had before pollution from Rome’s heavy traffic coated it with black particles.
She said: “These are the colours that tell the Colosseum’s story, like a lady’s grey hair.”Ms Conti added that detergents, which would have cut through the colours, had been banned from the job.
The Colosseum was the biggest Roman amphitheatre. It opened in 80AD and packed in crowds for 500 years, offering gladiator battles, animal hunting and even fake sea battles, with massive awnings drawn over the open roof to protect the 35,000-strong crowd from the sun.
Restorers are now slowly working their way round the monument’s 22 sets of three-tiered travertine arches, before setting to work on 58 sets of Roman brick arches, which have been exposed where the original facade has crumbled over the centuries.
Ms Conti said scraping off the crusts left by pollution was not just a question of appearance.
She added: “Under the crust, the pollution combines with water to form sulphuric acid which reduces the stone to chalk – what we call stone ‘cancer’. Lichen also grows under there, damaging the stone.”
Speaking from the top of the 157ft high building, she said: “Up here is where the women came to sit, far from what went on below.
“The arches at ground level did a good job of channelling people to their seats, but were a popular place for fighting and having sex.
“The Latin word for arch is fornix, which was the origin of the word ‘fornicate’.”
Further evidence of the bawdy atmosphere at the Colosseum was the discovery last year in an internal corridor of the frequent inscribing of phallus designs during the Roman era.
With the downfall of the Roman empire, the Colosseum fell into disrepair in the sixth century.
Under a sponsorship deal, the clean-up is being paid for by Italian shoe maker Tod’s, to be followed by another €15m (£12m) from the firm to build a visitor centre and continue restoration.