Officers on patrol in the capital's historic centre discovered the man preparing to climb the famous fountain and ordered him to come down, but according to Ansa he persisted in his attempt.
Once the man, said to be in his 40s, was stopped and questioned, police slapped him with an on-the-spot fine of €500 under city ordinances that ban the public from sneaking into, clambering upon or otherwise endangering Rome's historic landmarks.
He also faces a ticket for failing to show police a valid ID.
Rome's heritage authorities have been informed and are checking the fountain for damage.
The iconic water feature has weathered assaults before, including visitors' many attempts to recreate Anita Ekberg's famous splash in La Dolce Vita – with or without their clothes.
Its waters have also been dyed red twice, both times by the same Italian "vandalism artist" who claimed he was protesting the cost of Rome's film festival.
Photo: Christophe Simon/AFP
Bad behaviour tends to multiply in the warmer months, as the temperature climbs and a dip in one of Rome's marble fountains becomes more tempting than ever.
The city deploys special monitors at some of its most famous monuments, including the Trevi fountain, to watch out for anyone bathing their feet or picnicking.
Earlier this month the chairman of AS Roma, American-Italian businessman James Pallotta, was fined for celebrating his team's surprise victory over Barcelona with a backwards somersault into the Fontana dei Leoni in Piazza del Popolo. The remorseful billionaire subsequently offered to donate €230,000 towards the restoration of another Roman fountain, the Fontana del Pantheon in front of the capital's ancient former temple.
Rome isn't the only Italian city that faces a problem with unruly visitors. Venice has long battled to protect its landmarks from the tourist crowds, and last week the city's mayor threatened legal action after tourists were filmed diving off the Rialto Bridge into the Grand Canal.
- Rome begins crackdown on bad behaviour at Trevi Fountain
- Ekberg wannabe recreates La Dolce Vita dip
- How bad-mannered tourists are riling Venice
Photo: Andreas Solaro/AFP